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1

Spectroscopy and Reactions of Molecules Important in Chemical Evolution.  

National Technical Information Service (NTIS)

The research includes: (1) hot hydrogen atom reactions in terms of the nature of products produced, mechanism of the reactions and the implication and application of such reactions for molecules existing in interstellar clouds, in planetary atmospheres, a...

R. S. Becker

1974-01-01

2

Chemical Reactions  

NSDL National Science Digital Library

We don't often stop to think about it, but underlying many of our everyday activities are chemical reactions. From the cooking of an egg to the growth of a child, chemical reactions make things happen. Although many of the reactions that support our lives

National Science Teachers Association (NSTA)

2009-05-01

3

Microfluidic chemical reaction circuits  

DOEpatents

New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

Lee, Chung-cheng (Irvine, CA); Sui, Guodong (Los Angeles, CA); Elizarov, Arkadij (Valley Village, CA); Kolb, Hartmuth C. (Playa del Rey, CA); Huang, Jiang (San Jose, CA); Heath, James R. (South Pasadena, CA); Phelps, Michael E. (Los Angeles, CA); Quake, Stephen R. (Stanford, CA); Tseng, Hsian-rong (Los Angeles, CA); Wyatt, Paul (Tipperary, IE); Daridon, Antoine (Mont-Sur-Rolle, CH)

2012-06-26

4

Chemical Reactions (Netorials)  

NSDL National Science Digital Library

Chemical Reactions: this is a resource in the collection "Netorials". The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.

5

Chemical Reaction Problem Solving.  

ERIC Educational Resources Information Center

|Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

Veal, William

1999-01-01

6

Nonadiabatic chemical reactions  

Microsoft Academic Search

A mixed quantum-classical approach where the environment is treated classically and the reactive degrees of freedom are considered to be quantum mechanical can be used to describe many chemical reactions, such as proton and electron transfer processes. We present reactive flux correlation function expressions for the rate constants of nonadiabatic chemical reactions occurring in quantum-classical systems. By means of a

Alessandro Sergi; Raymond Kapral

2005-01-01

7

Spectroscopic and Photochemical Study of Molecules Important in Chemical Evolution.  

National Technical Information Service (NTIS)

The primary broad goals of this research are to investigate (1) the possible reactions responsible for generation of compounds important in chemical evolution, and (2) reactions of compounds important in chemical evolution. In both cases the interest incl...

R. S. Becker

1973-01-01

8

Rates of Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the third of four Science Objects in the Chemical Reactions SciPack. It demonstrates

National Science Teachers Association (NSTA)

1900-01-01

9

Chemical Reactions in DSMC  

SciTech Connect

DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

Bird, G. A. [GAB Consulting Pty Ltd, 144/110 Sussex Street, Sydney NSW 2000 (Australia)

2011-05-20

10

Critical Evaluation of Chemical Reaction Rates and Collision Cross Sections of Importance in the Earth's Upper Atmosphere and the Atmospheres of Other Planets, Moons, and Comets  

NASA Astrophysics Data System (ADS)

We recommend establishment of a long-term program of critical evaluation by domain experts of the rates and cross sections of atomic and molecular processes that are needed for understanding and modeling the atmospheres in the solar system. We envision products resembling those from the ongoing JPL/NASA Panel for Data Evaluation and the efforts of the international combustion modeling community funded by US DOE and its European counterpart. Both of these endeavors already provide some important inputs for modeling the atmospheres of the Earth, planets, moons, and comets. However, their applications restrict the choice of which processes to evaluate and the temperature and pressure ranges to cover, thus leaving large gaps that need to be filled. Interestingly, an older evaluation program once filled some of these gaps. Funded by the US DoD in the 1960s-1980s, the DNA Reaction Rate Handbook provided a thorough treatment of numerous types of collisions and reactions that are important in the Earth's lower ionosphere, and the program even provided funding for new laboratory measurements. Other examples could be given, with the on-line resources at NIST being among the best, but most provide a narrower scope or less critical evaluation. What is needed is not a just a list of processes and numbers (i.e., a "database"), but rather serious comparison of the available information and specific statements from independent expert laboratory/theory data providers about what should be believed, what uncertainty to assign, and what is most in need of redetermination. The major topic areas would include the following: 1. Chemical reactions of neutral atoms and molecules in their ground electronic states 2. Ion-molecule reactions 3. Chemistry, relaxation, and radiation of electronically excited atoms and molecules 4. Vibrational and rotational relaxation and radiation 5. Photoabsorption, photodissociation, and photoionization 6. Electron-impact excitation, dissociation, ionization, and recombination 7. Energetic heavy particle excitation and charge exchange

Huestis, D. L.

2005-05-01

11

Magnetic Effects in Chemical Reactions  

Microsoft Academic Search

The Review discusses in what elementary chemical reactions the intrinsic angular momentum of electrons and nuclei is conserved and in what reactions it is not conserved, how weak electron-nuclear magnetic interaction and an external magnetic field influence the conservation of angular momentum and what are the consequences of this effect, and what magnetic effects occur in chemical reactions, as well

Anatolii L Buchachenko

1976-01-01

12

Chemical Reactions: Investigating Exothermic and Endothermic Reactions  

NSDL National Science Digital Library

This activity is an inquiry-based investigation where students discover the indicators of chemical reactions (endothermic and exothermic) by collecting data and using that data to develop a testable question for further experimentation.

13

Bistable and oscillating chemical reactions  

NASA Astrophysics Data System (ADS)

In the last decade the number and the diversity of isothermal oscillating reactions in homogeneous aqueous solution have tremendously increased. We present an updated classified review of these chemical reactions.

Pacault, A.; Ouyang, Q.; de Kepper, P.

1987-09-01

14

Continuous chemical reaction chromatography  

SciTech Connect

The past three years have been devoted to investigating simulated countercurrent chomatographic moving bed separators (SCMCS) and simulated countercurrent moving bed reactors (SCMCR). These are novel separators and reactors used for separation, or for carrying out a chemical reaction and separation continuously and simultaneously in fixed bed. In the SCMCR and the SCMCS the process aspects of a countercurrent moving bed, in which a stream of solids flows countercurrent to an inert fluid and past stationary reactant inlet, is simulated by successively switching feed and product take-off streams through a series of inlets located at fixed intervals along a fixed bed or between a series of packed columns. The flow of solids past a fixed feed point, characteristic of countercurrent moving beds, is replaced by motion of the feed past a fixed packed bed. Feed enters a particular column for a fixed length of time, and then is switched to the next column. Product streams are also advanced simultaneously. When the feed point has progressed to the end it is returned to the starting position and the process repeated. The shifting of the feed and the product positions in the direction of fluid flow thus simulates the movement of solids in the opposite direction. The requisite motion between the feed and the bed, which is continuous for true countercurrency, is replaced by periodic, discrete steps in simulated countercurrency. The continuous, steady state operation characteristic of true countercurrency is replaced by periodic transients at each switch of the feed.

Aris, R.; Carr, R.W.

1992-01-01

15

Chemical Biology\\/ Chemical Genetics\\/ Chemical Genomics: Importance of Chemical Library  

Microsoft Academic Search

A new field of science, chemical biology\\/ chemical genetics\\/ chemical genomics (cb\\/cg\\/cg) has emerged since the late 1990's, especially in the United States. The NIH Roadmap agenda, Molecular Libraries Screening Center Network (MLSCN), became a drive force to push cb\\/cg\\/cg forward. Cb\\/cg\\/cg studies consist of three methodologies, chemical libraries with small molecules, high-throughput screenings, and computational databases. In this review,

Fumihiko Kugawa; Masaru Watanabe; Fuyuhiko Tamanoi

2007-01-01

16

Monotonicity in chemical reaction systems  

Microsoft Academic Search

This article discusses the question of when the dynamical systems arising from chemical reaction networks are monotone, preserving an order induced by some proper cone. The reaction systems studied are defined by the reaction network structure while the kinetics is only constrained very weakly. Necessary and sufficient conditions on cones preserved by these systems are presented. Linear coordinate changes which

Murad Banaji

2009-01-01

17

Chemical reaction on polysaccharides  

Microsoft Academic Search

The article discusses the synthesis of pullulan derivatives containing chloroalkyl groups by the reaction of crosslinked pullulan microparticles with different chloroalkyl chlorides in organic basic solvents. These new products may allow the attachment of various bioactive compounds by covalent bonding.

G Mocanu; D Vizitiu; D Mihai; A Carpov

1999-01-01

18

Chemical burn or reaction  

MedlinePLUS

... the skin has come in contact with the toxic substance Rash , blisters , burns on the skin Unconsciousness ... locked cabinet. Avoid mixing different products that contain toxic chemicals such as ammonia and bleach. The mixture ...

19

Speeding chemical reactions by focusing  

NASA Astrophysics Data System (ADS)

We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system parameters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate ~t-1/2 to very close to the perfect mixing rate, ~t-1.

Lacasta, A. M.; Ramírez-Piscina, L.; Sancho, J. M.; Lindenberg, K.

2013-04-01

20

Insights into the mechanisms on chemical reactions: reaction paths for chemical reactions. [Li + HF; OH + Hâ  

Microsoft Academic Search

We report reaction paths for two prototypical chemical reactions: Li + HF, an electron transfer reaction, and OH + Hâ, an abstraction reaction. In the first reaction we consider the connection between the energetic terms in the reaction path Hamiltonian and the electronic changes which occur upon reaction. In the second reaction we consider the treatment of vibrational effects in

T. H. Jr. Dunning; E. Rosen; R. A. Eades

1987-01-01

21

Modeling and Simulating Chemical Reactions  

Microsoft Academic Search

Abstract Many students are familiar with the idea of modeling chemical reactions in terms of ordinary dieren tial equations. However, these deterministic reaction rate equations are really a certain large-scale limit of a sequence of ner-scale probabilistic models. In studying this hierarchy of models, students can be exposed to a range of modern ideas in applied and compu- tational mathematics.

Desmond J. Higham

2008-01-01

22

Millisecond chemical reactions and reactors  

Microsoft Academic Search

Short contact time chemical reactors have many features which are very different from conventional packed bed reactors in that temperatures are determined by inlet parameters only, performance is nearly unchanged over wide variations in flow rate, and highly nonequilibrium products can be obtained at high conversions. Chemical reactions occur in regions of large gradients in composition and temperature, so the

Lanny D. Schmidt

2000-01-01

23

Chemical Dynamics Special Feature: Chemical reaction dynamics  

Microsoft Academic Search

Understanding the motions of the constituent atoms in reacting molecules lies at the heart of chemistry and is the central focus of chemical reaction dynamics. The most detailed questions one can ask are about the evolution of molecules prepared in a single quantum state to products in individual states, and both calculations and experiments are providing such detailed understanding of

F. Fleming Crim

2008-01-01

24

Programmability of Chemical Reaction Networks  

NASA Astrophysics Data System (ADS)

Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

25

Chemical reaction rates and solvent friction  

SciTech Connect

The role of the dynamic solvent friction in influencing the rates of chemical reactions in solution is described. Features considered include (a) the bias of the reaction coordinate toward a direction of lesser friction in the diffusive limit, (b) the importance of frequency-dependent friction in atom transfers, tunneling reactions and isomerizations, (c) the dynamic nonequilibrium solvation in charge transfers which leads to a polar solvent molecule reorientation time dependence for the rate, and (d) the importance of internal degrees of freedom in the location of the Kramers turnover for isomerizations.

Hynes, J.T.

1986-01-01

26

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

|Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

27

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

28

Infrared Laser Catalyzed Chemical Reactions  

Microsoft Academic Search

The development of the laser some twelve years ago has resulted in the creation and\\/or the resuscitation of a number of experimental disciplines involving measurements of energy transfer, chemical reaction rates, high resolution spectroscopy as well as nonlinear effects. In the last three years more and more work involving the use of lasers has been reported on in the literature

A. M. Ronn

1975-01-01

29

Chemical reaction and reactor engineering  

SciTech Connect

This book discusses research and design problems, simplifying reactor design considerations such as choice of reactor configuration, optimization, and scaleup, and modern surface analysis techniques for interpreting catalytic phenomena, and deciding on the most advantageous method for the selection, testing, development, and application of catalysts. It also covers how to develop models and formulate design strategies for gas-solid catalytic and noncatalytic reactions, overcoming such obstacles as complex hydrodynamics and inaccurate chemical kinetics in the modeling of fixed-bed catalytic processes.

Carberry, J.J.; Varma, A.

1987-01-01

30

Binary counting with chemical reactions.  

PubMed

This paper describes a scheme for implementing a binary counter with chemical reactions. The value of the counter is encoded by logical values of "0" and "1" that correspond to the absence and presence of specific molecular types, respectively. It is incremented when molecules of a trigger type are injected. Synchronization is achieved with reactions that produce a sustained three-phase oscillation. This oscillation plays a role analogous to a clock signal in digital electronics. Quantities are transferred between molecular types in different phases of the oscillation. Unlike all previous schemes for chemical computation, this scheme is dependent only on coarse rate categories for the reactions ("fast" and "slow"). Given such categories, the computation is exact and independent of the specific reaction rates. Although conceptual for the time being, the methodology has potential applications in domains of synthetic biology such as biochemical sensing and drug delivery. We are exploring DNA-based computation via strand displacement as a possible experimental chassis. PMID:21121058

Kharam, Aleksandra; Jiang, Hua; Riedel, Marc; Parhi, Keshab

2011-01-01

31

Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions  

PubMed Central

Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions.

SUZUKI, Toshinori

2013-01-01

32

Temperature-compensated chemical reactions  

NASA Astrophysics Data System (ADS)

Circadian rhythms are daily oscillations in behaviors that persist in constant light/dark conditions with periods close to 24h . A striking feature of these rhythms is that their periods remain fairly constant over a wide range of physiological temperatures, a feature called temperature compensation. Although circadian rhythms have been associated with periodic oscillations in mRNA and protein levels, the question of how to construct a network of chemical reactions that is temperature compensated remains unanswered. We discuss a general framework for building such a network.

Rajan, Kanaka; Abbott, L. F.

2007-02-01

33

Learning to predict chemical reactions.  

PubMed

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

2011-09-02

34

Chemical reactions of organic compounds on clay surfaces  

SciTech Connect

Chemical reactions of organic compounds including pesticides at the interlayer and exterior surfaces of clay minerals and with soil organic matter are reviewed. Representative reactions under moderate conditions possibly occurring in natural soils are described. Attempts have been made to clarify the importance of the chemical nature of molecules, their structures and their functional groups, and the Broensted or Lewis acidity of clay minerals.

Soma, Yuko; Soma, Mitsuyuki (National Institute for Environmental Studies, Ibaraki (Japan))

1989-11-01

35

Chemical reactions of organic compounds on clay surfaces.  

PubMed Central

Chemical reactions of organic compounds including pesticides at the interlayer and exterior surfaces of clay minerals and with soil organic matter are reviewed. Representative reactions under moderate conditions possibly occurring in natural soils are described. Attempts have been made to clarify the importance of the chemical nature of molecules, their structures and their functional groups, and the Brönsted or Lewis acidity of clay minerals.

Soma, Y; Soma, M

1989-01-01

36

The effect of chemical reaction on liquid round free jet  

Microsoft Academic Search

In the fluid engineering field, chemical reaction frequently occur. Sodium-water chain reaction in the sodium cooled nuclear reactor can make an explosion that causes the accident during the operation of nuclear reactor. Therefore, it is very important to investigate the characteristic of this chemically reacting type of jet to achieve the reliable design of industrial reactor. Although a number of

Seong Dae Hong; Okamoto Koji; Madarame Haruki

2002-01-01

37

Observation of Individual Chemical Reactions in Solution  

Microsoft Academic Search

Discrete chemical reaction events occurring in solution have been observed by single photon detection of a bimolecular, chemiluminescent reaction. The reactants were generated from 9,10-diphenylanthracene in acetonitrile with potential pulses applied to an ultramicroelectrode. Electrogenerated radical ions of opposite sign react to yield the excited singlet state of the parent compound. The chemical reactions were restricted to a 20-femtoliter volume

Maryanne M. Collinson; R. Mark Wightman

1995-01-01

38

Chemical reaction in a thermal plasma  

Microsoft Academic Search

A thermal plasma has high potential to instigate a refractory chemical reaction because it has a high temperature and high energy. So thermal plasmas have been utilized for some high-temperature processes in which a chemical reaction occurs, although so far chemical application of thermal plasmas has not been sufficient and their use should be promoted more. In this paper, the

Atsushi Kanzawa

1993-01-01

39

Nuclear physics reactions of astrophysical importance  

NASA Astrophysics Data System (ADS)

Understanding the origin of elements in the universe is one of the main goals of nuclear science and astrophysics today. Achieving this goal involves determining how the elements and their isotopes formed and being able to predict their abundances. At the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL), an experimental program has been established to use transfer reactions (such as (p,d) or (d,p)) to study the properties of many nuclei important to understanding the origins of various elements. Three measurements were done to aid in the determination of the origins of different light isotopes. Big Bang Nucleosynthesis calculations, constrained by the Wilkinson Microwave Anisotropy Probe results, produce primordial 7Li abundances almost a factor of four larger than those extrapolated from observations. Since primordial 7Li is believed to be mostly produced by the beta decay of 7Be, one proposed solution to this discrepancy is a resonant enhancement of the 7Be(d, p)2? reaction rate through the 5/2+ 16.7-MeV state in 9B. The 2H(7Be,d) 7Be reaction was used to search for such a resonance; none was observed. An upper limit on the width of the proposed resonance was deduced. 19F is believed to have formed in Asymptotic Giant Branch stars, but current models cannot reproduce the observed abundances of this nucleus. One of the key reactions responsible for the creation of 19F is 15N(?,?). Therefore, it is important to understand reactions that might destroy 15N, such as 15N(n,?). The magnitude of the 15N( n,?) reaction rate depends directly on the neutron spectroscopic factors of low-lying 16N levels. Currently the measured spectroscopic factors differ from those expected from theory by a factor of 2. A study has been done to resolve this discrepancy using the d( 15N,p) reaction. The spectroscopic factors were all found to be close to unity which is in agreement with theoretical predictions. In novae, gamma ray emission is believed to be primarily due to electron-positron annihilation, though the source of these positrons remains a mystery. The positrons are believed to originate from the beta decay of 18F due to its long half-life (t1/2 ˜ 110 min.). To date, gamma rays from this nucleus have not been observed. Therefore, studies have been made on reactions believed to destroy 18F, such as 18F(p,?) which goes through states in 19Ne. A recent study by Adekola et al. showed that a state at 6.289-MeV in 19Ne, just below the proton threshold, could have a significant impact on this reaction rate. However, the spin of this state could not be determined. To determine the spin of this sub-threshold state, a study of the 20Ne(p,d ) reaction was made using a proton beam on a carbon foil implanted with 20Ne. Due target contaminants, a spin assignment could not be made, but a new experimental design was created and is described in this dissertation.

O'Malley, Patrick D.

40

Theoretical Studies of Chemical Reactions: Dynamics.  

National Technical Information Service (NTIS)

Theoretical studies have been performed on the dynamics of interesting chemical reactions. The systems studied included the recombination reaction of methyl radicals to form ethylene, the addition of hydrogen atoms to carbon monoxide and the thermal disso...

A. F. Wagner M. J. Davis G. C. Schatz R. J. Duchovic R. Steckler

1988-01-01

41

Kinetics of Chemical Reactions in Foods  

Microsoft Academic Search

Chemical reactions occur in foods during processing and storage. Some reactions result in a quality loss and must be minimized,\\u000a whereas others result in the formation of a desired flavor or color and must be optimized to obtain the best product quality.\\u000a Kinetics is a science that involves the study of chemical reaction rates and mechanisms. An understanding of reaction

Romeo T. Toledo

42

Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions  

ERIC Educational Resources Information Center

|A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

Schultz, Emeric

2008-01-01

43

2005 Chemical Reactions at Surfaces  

SciTech Connect

The Gordon Research Conference (GRC) on 2005 Chemical Reactions at Surfaces was held at Ventura Beach Marriott, Ventura California from February 13, 2005 through February 18, 2005. The Conference was well-attended with 124 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.

Cynthia M. Friend

2006-03-14

44

When do chemical reactions promote mixing?  

Microsoft Academic Search

This paper reviews various situations, in which a chemical reaction promotes the mixing (of reactants and products) in an unstirred reactor. One example is an exothermic chemical reaction, which of course increases the local temperature of an unstirred reacting fluid and hence decreases the density. This can produce natural convection. Thus if the walls of the reactor are cooled, there

T. P. Ivleva; A. G. Merzhanov; E. N. Rumanov; N. I. Vaganova; A. N. Campbell; A. N. Hayhurst

2011-01-01

45

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The stoichiometric coefficients for a chemical equation are determined by comparing the slopes of concentration-time plots for the reactants and products. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

46

Microfabricated electrochemiluminescence cell for chemical reaction detection  

DOEpatents

A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA); Hsueh, Yun-Tai (Davis, CA); Smith, Rosemary L. (Davis, CA)

2003-01-01

47

Chemical Reactions in High-Speed Flows  

Microsoft Academic Search

Hypersonic flows are distinguished by a capacity to provoke endothermic chemical reactions in their constituent molecules. Interactions of gas-flow and chemical activity also take place in combustible (exothermic) gas mixtures, such as may be found in propulsive devices. After a brief validation of the idea that chemically active flows can be adequately treated via Euler-Prandtl theory, the paper is devoted

J. F. Clarke

1991-01-01

48

Dynamics in Tangible Chemical Reactions  

Microsoft Academic Search

Spatial understanding and the understanding of dynamic change in the spatial structure of molecules during a reaction is essen- tial for designing new molecules. Knowing the physical processes in the reactions helps to speed up the designing process. To support the designer with the correct representation of the designed molecule as well as showing the dynamic behavior of the whole

Patrick Maier; Marcus T; Gudrun Klinker

49

Conservation-dissipation structure of chemical reaction systems  

NASA Astrophysics Data System (ADS)

In this Brief Report, we show that balanced chemical reaction systems governed by the law of mass action have an elegant conservation-dissipation structure. From this structure a number of important conclusions can be easily deduced. In particular, with the help of this structure we can rigorously justify the classical partial equilibrium approximation in chemical kinetics.

Yong, Wen-An

2012-12-01

50

Microfabricated sleeve devices for chemical reactions  

DOEpatents

A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA)

2003-01-01

51

Regimes of chemical reaction waves initiated by nonuniform initial conditions for detailed chemical reaction models  

NASA Astrophysics Data System (ADS)

Regimes of chemical reaction wave propagation initiated by initial temperature nonuniformity in gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied using a multispecies transport model and a detailed chemical model. Possible regimes of reaction wave propagation are identified for stoichiometric hydrogen-oxygen and hydrogen-air mixtures in a wide range of initial pressures and temperature levels, depending on the initial non-uniformity steepness. The limits of the regimes of reaction wave propagation depend upon the values of the spontaneous wave speed and the characteristic velocities of the problem. It is shown that one-step kinetics cannot reproduce either quantitative neither qualitative features of the ignition process in real gaseous mixtures because the difference between the induction time and the time when the exothermic reaction begins significantly affects the ignition, evolution, and coupling of the spontaneous reaction wave and the pressure wave, especially at lower temperatures. We show that all the regimes initiated by the temperature gradient occur for much shallower temperature gradients than predicted by a one-step model. The difference is very large for lower initial pressures and for slowly reacting mixtures. In this way the paper provides an answer to questions, important in practice, about the ignition energy, its distribution, and the scale of the initial nonuniformity required for ignition in one or another regime of combustion wave propagation.

Liberman, M. A.; Kiverin, A. D.; Ivanov, M. F.

2012-05-01

52

Chemical Reactions and the Overhead Projector.  

ERIC Educational Resources Information Center

|Describes the construction of a simple apparatus that can be used to take advantage of the overhead projector in a spectacular presentation of chemical reactions that complement quantitative approaches of study in the traditional high school science classroom. (JRH)|

Papageorgiou, George; Xenos, John

1996-01-01

53

FAST ELEMENTARY STEPS IN CHEMICAL REACTION MECHANSIMS  

Microsoft Academic Search

A review is presented of studies of fast chemical reaction steps which ; were studied using various relaxation techniques. These studies include ligand ; substitution in metal complexes, proton transfer, and enzymatic hydrolysis. ; (D.L.C.);

M. Eigen

1963-01-01

54

Chemical Reaction Dynamics in Nanoscale Environments.  

National Technical Information Service (NTIS)

The major focus of the research in this program is the study of the behavior of molecular systems confined in nanoscale environments. The goal is to develop a theoretical framework for predicting how chemical reactions occur in nanoscale environments. To ...

E. M. Goldfield H. B. Schlegel W. L. Hase

2006-01-01

55

Aerosol Simulation Including Chemical and Nuclear Reactions.  

National Technical Information Service (NTIS)

The numerical simulation of aerosol transport, including the effects of chemical and nuclear reactions presents a challenging dynamic accounting problem. Particles of different sizes agglomerate and settle out due to various mechanisms, such as diffusion,...

E. C. Lemmon E. S. Marwil

1985-01-01

56

Chemical reactions in quantum crystals  

Microsoft Academic Search

Solid parahydrogen, known as a quantum crystal, is a novel matrix for the study of physical and chemical processes of molecules at low temperatures by high-resolution infrared spectroscopy. Ro-vibrational motion of molecules embedded in solid parahydrogen is well quantized on account of the weak interaction in the crystal. In addition, molecules are almost free from the cage effect because of

Takamasa Momose; Mizuho Fushitani; Hiromichi Hoshina

2005-01-01

57

Determining Interconnections in Chemical Reaction Networks  

Microsoft Academic Search

We present a methodology for robust determination of chemical reaction network interconnections. Given time series data that are collected from experiments and taking into account the measurement error, we minimize the 1-norm of the decision variables (reaction rates) keeping the data in close Euler-flt with a general model structure based on mass action kinetics which models the species' dynamics. We

Antonis Papachristodoulou; Ben Recht

2007-01-01

58

Chemical Principles Revisited: Annotating Reaction Equations.  

ERIC Educational Resources Information Center

Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

Tykodi, R. J.

1987-01-01

59

Chemical Principles Revisited: Annotating Reaction Equations.  

ERIC Educational Resources Information Center

|Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

Tykodi, R. J.

1987-01-01

60

Entropy Generation in a Chemical Reaction  

ERIC Educational Resources Information Center

|Entropy generation in a chemical reaction is analysed without using the general formalism of non-equilibrium thermodynamics at a level adequate for advanced undergraduates. In a first approach to the problem, the phenomenological kinetic equation of an elementary first-order reaction is used to show that entropy production is always positive. A…

Miranda, E. N.

2010-01-01

61

Novel variational principles of chemical reaction  

Microsoft Academic Search

Minimum principles of chemical reaction coordinates are established. IRC (intrinsic reaction coordinate) draws the path of minimum distance from reactant to product. The distance is measured in the rigged configuration Riemannian space whose metric is determined by the distribution of the adiabatic potential energy. Moreover, minimum property of the intrinsic principle of least action is established for the intrinsic dynamism

Akitomo Tachibana; Kenichi Fukui

1980-01-01

62

Chemical Reactions Among Indoor Pollutants  

Microsoft Academic Search

\\u000a Chemistry takes place all around us, regulating the intensity and nature of our exposure to pollutants in water, air and soil.\\u000a In indoor environments, chemistry can significantly alter the composition of the air we breathe. Transformations reduce our\\u000a exposure to reactants and increase our exposure to products. If this reaction takes place on or in a surface, the relative\\u000a exposure

Glenn Morrison

63

Concerted reactions of polynuclear metalloenzymes and their functional chemical models  

NASA Astrophysics Data System (ADS)

The mechanisms of the many-electron oxidation of water by a chemical model of the manganese oxidase cofactor in photosynthesis photosystem II (manganese(IV) clusters) and nitrogen reduction in chemical models of nitrogenase cofactor (vanadium(II) and molybdenum(III) clusters) were considered. The hypothesis was suggested according to which polynuclear enzyme cofactors and their functional chemical models performed two important functions, catalyzed noncomplementary processes and effected many-substrate concerted reactions with decreased activation energies.

Dzhabiev, T. S.; Shilov, A. E.

2011-03-01

64

40 CFR 799.19 - Chemical imports and exports.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Chemical imports and exports. 799.19 Section...CONTINUED) IDENTIFICATION OF SPECIFIC CHEMICAL SUBSTANCE AND MIXTURE TESTING REQUIREMENTS General Provisions § 799.19 Chemical imports and exports. Persons...

2013-07-01

65

Fluid flow and chemical reaction kinetics in metamorphic systems  

SciTech Connect

The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

Lasaga, A.C.; Rye, D.M. (Yale Univ., New Haven, CT (United States))

1993-05-01

66

Two Examples of Deterministic versus Stochastic Modeling of Chemical Reactions  

NASA Astrophysics Data System (ADS)

The numerical simulation of chemical reactions can be carried out using deterministic or stochastic models. The deterministic simulation gives the average behavior of the system, which is a suitable representation of the reaction when the number of molecules involved is large. The stochastic simulation requires stronger mathematical foundations, mainly from probability theory but allows prediction of the so-called stochastic effects, which are relevant when the number of molecules is small. A more accurate representation of processes dependent on the behavior of a small number of molecules is of increasing importance in current chemistry and can be achieved through stochastic modeling. From an educational point of view, the simultaneous use of stochastic and deterministic models in the simulation of chemical reactions results in a better understanding of the chemical dynamics. The two approaches are reviewed in this paper by using two selected examples of chemical reactions and four MATLAB programs, which implement both the deterministic and stochastic modeling of the examples.

Mira, José; González Fernández, Camino; Martínez Urreaga, Joaquín

2003-12-01

67

Topologically invariant reaction coordinates for simulating multistate chemical reactions.  

PubMed

Evaluating free energy profiles of chemical reactions in complex environments such as solvents and enzymes requires extensive sampling, which is usually performed by potential of mean force (PMF) techniques. The reliability of the sampling depends not only on the applied PMF method but also the reaction coordinate space within the dynamics is biased. In contrast to simple geometrical collective variables that depend only on the positions of the atomic coordinates of the reactants, the E(gap) reaction coordinate (the energy difference obtained by evaluating a suitable force field using reactant and product state topologies) has the unique property that it is able to take environmental effects into account leading to better convergence, a more faithful description of the transition state ensemble and therefore more accurate free energy profiles. However, E(gap) requires predefined topologies and is therefore inapplicable for multistate reactions, in which the barrier between the chemically equivalent topologies is comparable to the reaction activation barrier, because undesired "side reactions" occur. In this article, we introduce a new energy-based collective variable by generalizing the E(gap) reaction coordinate such that it becomes invariant to equivalent topologies and show that it yields more well behaved free energy profiles than simpler geometrical reaction coordinates. PMID:23214508

Mones, Letif; Csányi, Gábor

2012-12-17

68

Chain reaction : chemical reactions, student reactions and mine  

Microsoft Academic Search

This article describes a primary school science unit on 'chemical and change' that the author presented after attending a professional development course. The article describes her detailed preparation, which was necessary to overcome her previous extremely negative attitude to science teaching. The article then describes the author's change in her attitude to teaching science, and the students' extremely positive attitudes

B Dinneen

2008-01-01

69

Plasmonic smart dust for probing local chemical reactions.  

PubMed

Locally probing chemical reactions or catalytic processes on surfaces under realistic reaction conditions has remained one of the main challenges in materials science and heterogeneous catalysis. Where conventional surface interrogation techniques usually require high-vacuum conditions or ensemble average measurements, plasmonic nanoparticles excel in extreme light focusing and can produce highly confined electromagnetic fields in subwavelength volumes without the need for complex near-field microscopes. Here, we demonstrate an all-optical probing technique based on plasmonic smart dust for monitoring local chemical reactions in real time. The silica shell-isolated gold nanoparticles that form the smart dust can work as strong light concentrators and optically report subtle environmental changes at their pinning sites on the probed surface during reaction processes. As a model system, we investigate the hydrogen dissociation and subsequent uptake trajectory in palladium with both "dust-on-film" and "film-on-dust" platforms. Using time-resolved single particle measurements, we demonstrate that our technique can in situ encode chemical reaction information as optical signals for a variety of surface morphologies. The presented technique offers a unique scheme for real-time, label-free, and high-resolution probing of local reaction kinetics in a plethora of important chemical reactions on surfaces, paving the way toward the development of inexpensive and high-output reaction sensors for real-world applications. PMID:23458121

Tittl, Andreas; Yin, Xinghui; Giessen, Harald; Tian, Xiang-Dong; Tian, Zhong-Qun; Kremers, Christian; Chigrin, Dmitry N; Liu, Na

2013-03-07

70

Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction  

NASA Astrophysics Data System (ADS)

A color-change reaction is described in which two colorless solutions are combined to afford a black mixture. Two more colorless solutions are combined to afford a white mixture. The black and white mixtures are then combined to afford a clear, colorless solution. The reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, vinegar, ammonia, bleach, Epsom salt, and laundry starch.

Wright, Stephen W.

2002-01-01

71

Programmable calculator and kinetics of chemical reactions  

Microsoft Academic Search

This paper suggests the use of simulation techniques using a programmable calculator in the study of chemical reactions.† This article does not deal with the use of programmable calculations for producing ‘experimental’ data (i.e. as a substitute for the laboratory). Readers interested in that direction may refer to [1]. Also, I would like to thank E. W. Jenkins of the

Amos Ehrlich

1980-01-01

72

Classification of Chemical Reactions: Stages of Expertise  

ERIC Educational Resources Information Center

|In this study we explore the strategies that undergraduate and graduate chemistry students use when engaged in classification tasks involving symbolic and microscopic (particulate) representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention when classifying…

Stains, Marilyne; Talanquer, Vicente

2008-01-01

73

Computer Animation of a Chemical Reaction.  

ERIC Educational Resources Information Center

|Taking a prototype chemical reaction (molecular hydrogen plus hydrogen atom), constructs an accurate semiempirical, generalized diatomics-in-molecules potential energy surface, calculates motions of these atoms on this surface using REACTS trajectory program, and presents results as moving picture on a microcomputer graphics system. Provides…

Eaker, Charles W.; Jacobs, Edwin L.

1982-01-01

74

Chemical Memory Reactions Induced Bursting Dynamics in Gene Expression  

PubMed Central

Memory is a ubiquitous phenomenon in biological systems in which the present system state is not entirely determined by the current conditions but also depends on the time evolutionary path of the system. Specifically, many memorial phenomena are characterized by chemical memory reactions that may fire under particular system conditions. These conditional chemical reactions contradict to the extant stochastic approaches for modeling chemical kinetics and have increasingly posed significant challenges to mathematical modeling and computer simulation. To tackle the challenge, I proposed a novel theory consisting of the memory chemical master equations and memory stochastic simulation algorithm. A stochastic model for single-gene expression was proposed to illustrate the key function of memory reactions in inducing bursting dynamics of gene expression that has been observed in experiments recently. The importance of memory reactions has been further validated by the stochastic model of the p53-MDM2 core module. Simulations showed that memory reactions is a major mechanism for realizing both sustained oscillations of p53 protein numbers in single cells and damped oscillations over a population of cells. These successful applications of the memory modeling framework suggested that this innovative theory is an effective and powerful tool to study memory process and conditional chemical reactions in a wide range of complex biological systems.

Tian, Tianhai

2013-01-01

75

Documentation of Chemical Reactions. I. A Faceted Classification  

ERIC Educational Resources Information Center

Existing methods for coding chemical compounds are discussed and evaluated as to their suitability for documentation of chemical reactions, a new classification for chemical reactions is presented, and possibilities of automatic encoding are studied. (24 references) (Author)

Osinga, M.; Verrijn Stuart, A. A.

1973-01-01

76

Chemical reaction engineering using molecularly imprinted polymeric catalysts  

Microsoft Academic Search

Enzymes play an important role as highly specific catalysts in biotechnology [J. Biotechnol. 66 (1998) 3; Hydrolases in Organic Synthesis, Wiley, New York, 1999] as well as in chemical reaction engineering [J. Biotechnol. 59 (1997) 11; Trends Biotechnol. 13 (7) (1995) 253]. However, the drawbacks of these biomaterials are poor durability and relatively high costs of production. Thus, the technique

Oliver Brüggemann

2001-01-01

77

Neutral theory of chemical reaction networks  

NASA Astrophysics Data System (ADS)

To what extent do the characteristic features of a chemical reaction network reflect its purpose and function? In general, one argues that correlations between specific features and specific functions are key to understanding a complex structure. However, specific features may sometimes be neutral and uncorrelated with any system-specific purpose, function or causal chain. Such neutral features are caused by chance and randomness. Here we compare two classes of chemical networks: one that has been subjected to biological evolution (the chemical reaction network of metabolism in living cells) and one that has not (the atmospheric planetary chemical reaction networks). Their degree distributions are shown to share the very same neutral system-independent features. The shape of the broad distributions is to a large extent controlled by a single parameter, the network size. From this perspective, there is little difference between atmospheric and metabolic networks; they are just different sizes of the same random assembling network. In other words, the shape of the degree distribution is a neutral characteristic feature and has no functional or evolutionary implications in itself; it is not a matter of life and death.

Lee, Sang Hoon; Bernhardsson, Sebastian; Holme, Petter; Kim, Beom Jun; Minnhagen, Petter

2012-03-01

78

Laboratory Studies of Homogeneous and Heterogeneous Chemical Processes of Importance in the Upper Atmosphere.  

National Technical Information Service (NTIS)

The objective of this study was to conduct measurements of chemical kinetics parameters for reactions of importance in the stratosphere and upper troposphere, and to study the interaction of trace gases with ice surfaces in order to elucidate the mechanis...

M. J. Molina

2003-01-01

79

Oscillations in a laser-induced chemical reaction: coupling of chemical reactions with an acoustic effect  

Microsoft Academic Search

An oscillatory phenomenon has been observed in a laser-induced photochemical reaction occurring in a degassed acetone or benzene solution of the complex [}Au[P(C6H4OMe-p)3{]2-(?-C?C)] after flash photolysis. It been confirmed that the observed oscillation is due to the chemical reactions coupling with the photoacoustic effect.

Yu-Xiang Weng; Hong Xiao; Kwok-Chu Chan; Chi-Ming Che

1997-01-01

80

Chemical and radiation-chemical radical reactions in lignocellulose materials  

NASA Astrophysics Data System (ADS)

Chemical and radiation-chemical radical reactions in lignocellulose materials were explored by 3-cm and 2-mm ESR spectroscopy. Background (intrinsic) singlet signals at g=2.003 from wood pulp and lignin and those arising during reaction of lignocellulose materials with acids and chlorine were attributed to radicals with conjugated C=C bonds. The 2-mm ESR signal with 3D anisotropy of g-factor from o-semiquinone radical ions formed in reaction of lignin with NaOH was recorded for the first time. The singlet signals derived from cellulose ?-irradiated at 77 K and marked out during post-thermal reactions were assigned to radicals with conjugated bonds. In wetted cellulose, a triplet signal with ??H?2.7 mT and imposed quadruplet structure (0.5-0.7 mT) from three ?-protons was detected at 300 K and attributed to ?4-radicals. The triplet signals derived from ?2- and ?3-radicals in pyranose cycles of cellulose exhibited higher values of ??H (3.0-3.2 mT) and lower thermal stability (up to 250 K). In radiolyzed cotton pulp, detected were ESR signals derived from formyl radicals formed upon rupture of the ?5=?6 bond in pyranose cycles. Heating up irradiated samples under ?2 was accompanied by formation of peroxide radicals. Photoinduced recombination of trapped electrons with ?1-radicals was found to proceed as a chain reaction with a kinetic length of about 25 units. Photolysis (??360 nm) of radiolyzed cellulose enhanced the disclosure of pyranose cycles and, as a result, the evolution of CO2 by a factor of 2-2.5.

Kuzina, Svetlana I.; Shilova, Irina A.; Mikhailov, Al'fa I.

2011-09-01

81

Effect of Chemical and Nuclear Reactions on Aerosol Transport.  

National Technical Information Service (NTIS)

The inclusion of the effects of chemical and nuclear reactions on aerosol transport is a complex problem in numerical simulation. Heterogeneous chemical reactions occur at the interface between the surface of a particle and the suspending medium, or betwe...

E. C. Lemmon E. S. Marwil

1984-01-01

82

Multiscale stochastic simulations of chemical reactions with regulated scale separation  

NASA Astrophysics Data System (ADS)

We present a coupling of multiscale frameworks with accelerated stochastic simulation algorithms for systems of chemical reactions with disparate propensities. The algorithms regulate the propensities of the fast and slow reactions of the system, using alternating micro and macro sub-steps simulated with accelerated algorithms such as ? and R-leaping. The proposed algorithms are shown to provide significant speedups in simulations of stiff systems of chemical reactions with a trade-off in accuracy as controlled by a regulating parameter. More importantly, the error of the methods exhibits a cutoff phenomenon that allows for optimal parameter choices. Numerical experiments demonstrate that hybrid algorithms involving accelerated stochastic simulations can be, in certain cases, more accurate while faster, than their corresponding stochastic simulation algorithm counterparts.

Koumoutsakos, Petros; Feigelman, Justin

2013-07-01

83

The role of chemical reactions in the Chernobyl accident  

SciTech Connect

It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80-110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000 Degree-Sign C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.

Grishanin, E. I., E-mail: egrishanin@orexovo.net [Russian Research Center Kurchatov Institute (Russian Federation)

2010-12-15

84

Noise-induced enhancement of chemical reactions in nonlinear flows.  

PubMed

Motivated by the problem of ozone production in atmospheres of urban areas, we consider chemical reactions of the general type: A+B-->2C, in idealized two-dimensional nonlinear flows that can generate Lagrangian chaos. Our aims differ from those in the existing work in that we address the role of transient chaos versus sustained chaos and, more importantly, we investigate the influence of noise. We find that noise can significantly enhance the chemical reaction in a resonancelike manner where the product of the reaction becomes maximum at some optimal noise level. We also argue that chaos may not be a necessary condition for the observed resonances. A physical theory is formulated to understand the resonant behavior. (c) 2002 American Institute of Physics. PMID:12779572

Liu, Zonghua; Lai, Ying-Cheng; Lopez, Juan M.

2002-06-01

85

Scattering Resonances in the Simplest Chemical Reaction  

NASA Astrophysics Data System (ADS)

Recent studies of state-resolved angular distributions show the participation of reactive scattering resonances in the simplest chemical reaction. This review is intended for those who wish to learn about the state-of-the-art in the study of the H + H2 reaction family that has made this breakthrough possible. This review is also intended for those who wish to gain insight into the nature of reactive scattering resonances. Following a tour across several fields of physics and chemistry where the concept of resonance has been crucial for the understanding of new phenomena, we offer an operational definition and taxonomy of reactive scattering resonances. We introduce simple intuitive models to illustrate each resonance type. We focus next on the last decade of H + H2 reaction dynamics. Emphasis is placed on the various experimental approaches that have been applied to the search for resonance behavior in the H + H2 reaction family. We conclude by sketching the road ahead in the study of H + H2 reactive scattering resonances.

Fernandez-Alonso, Felix; Zare, Richard N.

2002-10-01

86

Molecular Dynamics Simulations of Chemical Reactions for Use in Education  

ERIC Educational Resources Information Center

|One of the simulation engines of an open-source program called the Molecular Workbench, which can simulate thermodynamics of chemical reactions, is described. This type of real-time, interactive simulation and visualization of chemical reactions at the atomic scale could help students understand the connections between chemical reaction equations…

Qian Xie; Tinker, Robert

2006-01-01

87

Some chemical and mineralogical considerations important for understanding leachate chemistry  

SciTech Connect

Both the raw shale material and the retorting process parameters are influential in determining the subsequent behavior of the spent shale solids with respect to leaching and/or environmental weathering. The process parameters define the mineral reactions that occur to form the mineral assemblage in the spent shale, while the major and trace element residences and mobilities from the raw shale determine the extent of incorporation of these elements in the spent shale matrix and ultimately the composition of leachate generated by the spent shale solid: water interaction. In order to understand leachate compositions, it is necessary to determine this water: solid interaction, but the solid wastes being considered are a dependent function of the raw shale material and the process parameters. Thus, in order to understand the chemical principles operative in leachate generation, it is necessary to elucidate the interplay of the raw material and the process parameters in the formation of the waste and then the interaction of the waste form with water. The leachate and the solid waste are dependent variables, while the raw shale and the process parameters are independent variables. These considerations are illustrated by results of chemical characterization and experimental studies of field generated spent shales. Results from field generated materials are used to describe important considerations relative to the understanding of leachate chemistry.

Peterson, E.J.; Wagner, P.

1982-01-01

88

Organic chemical reactions in supercritical water  

SciTech Connect

Water near or above its critical point (374 C, 218 atm) is attracting increased attention as a medium for organic chemistry. Most of this new attention is driven by the search for more green or environmentally benign chemical processes. Using near-critical or supercritical water (SCW) instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution prevention. Interest in doing chemistry in SCW is not entirely new, however. There has been much previous research in this area with applications in synthetic fuels production, biomass processing, waste treatment, materials synthesis, and geochemistry. Water near its critical point possesses properties very different from those of ambient liquid water. The dielectric constant is much lower, and the number and persistence of hydrogen bonds are both diminished. As a result, high-temperature water behaves like many organic solvents in that organic compounds enjoy high solubilities in near-critical water and complete miscibility with SCW. Moreover, gases are also miscible in SCW so employing a SCW reaction environment provides an opportunity to conduct chemistry in a single fluid phase that would otherwise occur in a multiphase system under more conventional conditions. The paper discusses the use of supercritical water in the following reactions: hydrogenation/dehydrogenation; C-C bond formation; rearrangements; hydration/dehydration; elimination; hydrolysis; partial oxidation; H-D exchange; decomposition; and oxidation.

Savage, P.E. [Univ. of Michigan, Ann Arbor, MI (United States). Chemical Engineering Dept.

1999-02-01

89

Dynamical resonance in F+H 2 chemical reaction and rotational excitation effect  

Microsoft Academic Search

Reaction resonance is a frontier topic in chemical dynamics research, and it is also essential to the understanding of mechanisms\\u000a of elementary chemical reactions. This short article describes an important development in the frontier of research. Experimental\\u000a evidence of reaction resonance has been detected in a full quantum state resolved reactive scattering study of the F+H2 reaction. Highly accurate full

XueMing Yang; DaiQian Xie; DongHui Zhang

2007-01-01

90

Quantum theory of chemical reaction rates  

SciTech Connect

If one wishes to describe a chemical reaction at the most detailed level possible, i.e., its state-to-state differential scattering cross section, then it is necessary to solve the Schroedinger equation to obtain the S-matrix as a function of total energy E and total angular momentum J, in terms of which the cross sections can be calculated as given by equation (1) in the paper. All other physically observable attributes of the reaction can be derived from the cross sections. Often, in fact, one is primarily interested in the least detailed quantity which characterizes the reaction, namely its thermal rate constant, which is obtained by integrating Eq. (1) over all scattering angles, summing over all product quantum states, and Boltzmann-averaging over all initial quantum states of reactants. With the proper weighting factors, all of these averages are conveniently contained in the cumulative reaction probability (CRP), which is defined by equation (2) and in terms of which the thermal rate constant is given by equation (3). Thus, having carried out a full state-to-state scattering calculation to obtain the S-matrix, one can obtain the CRP from Eq. (2), and then rate constant from Eq. (3), but this seems like ``overkill``; i.e., if one only wants the rate constant, it would clearly be desirable to have a theory that allows one to calculate it, or the CRP, more directly than via Eq. (2), yet also correctly, i.e., without inherent approximations. Such a theory is the subject of this paper.

Miller, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States). Chemical Sciences Div.

1994-10-01

91

Silicon-based sleeve devices for chemical reactions  

DOEpatents

A silicon-based sleeve type chemical reaction chamber is described that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis. 32 figs.

Northrup, M.A.; Mariella, R.P. Jr.; Carrano, A.V.; Balch, J.W.

1996-12-31

92

Silicon-based sleeve devices for chemical reactions  

DOEpatents

A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA); Mariella, Jr., Raymond P. (Danville, CA); Carrano, Anthony V. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

1996-01-01

93

Modeling enzymatic reactions via chemical Langevin-Levy equation  

Microsoft Academic Search

Chemical Langevin Equation (CLE) describes a useful approximation in stochastic modeling of chemical reactions. CLE-based ?-leaping algoritm updates the quantities of every molecule in a reaction system with a period of ?, firing every reaction in the system so many times that the concentration of each molecule can be assumed to remain in the current concentration state. Substituting the Brownian

Mustafa A. Altinkaya; Ercan E. Kuruoglu

2012-01-01

94

Chemical reactions in reactive powder metal mixtures during shock compression  

Microsoft Academic Search

A heterogeneous chemical reaction model is proposed and used to describe shock-induced chemical reactions that occur in reactive granular mixtures during shock compression. The proposed heterogeneous model is intended for application in mesoscale simulations at locations where reactant particles are in contact. Previous studies have employed homogeneous reaction rate models with Arrhenius type kinetics, in which the material transport mechanism

D. J. Reding; S. Hanagud

2009-01-01

95

Development of the reaction time accelerating molecular dynamics method for simulation of chemical reaction  

Microsoft Academic Search

We present a novel and efficient method to integrate chemical reactions into molecular dynamics to simulate chemical reaction systems. We have dubbed this method RTAMD, an acronym for reaction time accelerating molecular dynamics. The methodology we propose here requires no more than the knowledge of the empirical intermolecular potentials for the species at play as well as the elementary reaction

Hiromitsu Takaba; Shigekazu Hayashi; Huifeng Zhong; Hema Malani; Ai Suzuki; Riadh Sahnoun; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Momoji Kubo; Carlos A. Del Carrpio; Akira Miyamoto

2008-01-01

96

On differential geometric formalization of chemical reaction kinetics statical aspects  

Microsoft Academic Search

In this article the basic mathematical structure of chemical reaction kinetics is investigated. For this purpose the methods of modern differential geometry are used. Using this approach the various aspects of species, reactions and stoichiometry can be separately treated.

L. Ropolyi; P. Réti

1984-01-01

97

Detecting strictly detailed balanced subnetworks in open chemical reaction networks  

Microsoft Academic Search

The notion “strictly detailed balanced subnetwork” is introduced, for chemical reaction networks which are open and spatially homogeneous, to refer to any set of reactions the net rates of which vanish in each asymptotically stable steady state, regardless of the kinetic parameters of any reaction in the whole network. Necessary and sufficient conditions for sets of reactions to be strictly

Stefan Schuster; Ronny Schuster

1991-01-01

98

Variability of the Cell Potential of a Given Chemical Reaction  

Microsoft Academic Search

It is demonstrated in this article that while the value of the free energy change for any chemical reaction is independent of path (a state function), the value of the standard cell potential of a reaction is dependent on the half-cell reactions used to carry out that reaction. That is, the standard cell potential is not a state function, but

Ladislav H. Berka; Ilie Fishtik

2004-01-01

99

Implementation of a vibrationally linked chemical reaction model for DSMC  

Microsoft Academic Search

A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more

A. B. Carlson; Graeme A. Bird

1994-01-01

100

Robust Stochastic Chemical Reaction Networks and Bounded Tau-Leaping  

Microsoft Academic Search

The behavior of some stochastic chemical reaction networks is largely unaffected by slight inaccuracies in reaction rates. We formalize the robustness of state probabilities to reaction rate deviations, and describe a formal connection between robustness and efficiency of simulation. Without robustness guarantees, stochastic simulation seems to require computational time proportional to the total number of reaction events. Even if the

David Soloveichik

2008-01-01

101

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Green chemical synthesis through catalysis and alternate reaction conditions Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

102

Investigating Factors Influencing Rates of Chemical Reactions  

NSDL National Science Digital Library

This activity is a lab investigation in which students observe the rate of generation of hydrogen gas from a reaction, and then modify the procedure to compare another variable affecting the rate of this reaction.

Derickson, Paula

103

Thermophoretic transport in impinging flows including chemical reactions  

NASA Astrophysics Data System (ADS)

The research constitutes a fundamental study of transport phenomena that has applications to the fabrication of optical fibers. The flow, heat and mass transfer with chemical reactions, and thermophoretic transport of silica particles are studied. The governing equations have been formulated and solved to determine the velocity, temperature and species concentrations, and the effects of buoyancy, variable properties, chemical reactions, and thermophoretic transport on deposition uniformity and efficiency. A path-line/stream-line approach for determining variable particle concentration stagnation deposition with thermophoretic transport is introduced. The research is of fundamental interest and has applications to optical fiber fabrication. A review of the thermophoresis phenomena is provided including a recommended treatment for the thermophoretic coefficient, K. A discussion of the related chemical reactions is given. A study of a H2-N 2 non-premixed jet flame is performed to appraise the proposed H2 oxidation reaction rate and heat release rate. The present results of the velocity and temperature distributions are in very good agreement with the published experimental data. A study of silica (SiO2) particle transport in a free jet system is carried out. The gas entrainment and the thermophoretic transport are two important parameters that determine the particle transport. Both non-reacting and reacting jet flows are studied. The effects of inclination of jet flows on particle transport are also studied. A path-line/stream-line approach for determining deposition with thermophoretic transport in stagnation flow is introduced. This approach allows a variable particle concentration inlet boundary condition to be used. A closed form solution is achieved using this approach. Numerical studies of deposition on a cylindrical preform for both non-reacting and reacting jets are also investigated. A study of a small scale fiber fabrication is made with a cylindrical preform and two burners. Of special interest are the effects of preform temperature and preform thermal conductivity on the deposition efficiency.

Hsu, Frank Kuan-Chao

104

Thermophoresis of an Aerosol Sphere with Chemical Reactions  

Microsoft Academic Search

The thermophoretic motion of a spherical aerosol particle undergoing a chemical reaction in a uniformly prescribed temperature gradient is studied theoretically in the quasisteady limit of negligible Peclet and Reynolds numbers. The chemical reaction taking place within the particle can be either endothermic or exothermic. The Knudsen number is assumed to be small (of the order 0.1) so that the

Tzu H. Hsieh; Huan J. Keh

2012-01-01

105

Synthesis of reactive distillation systems with multiple equilibrium chemical reactions  

Microsoft Academic Search

The authors describe a procedure to determine the feasibility of separating mixtures with multiple equilibrium chemical reactions by reactive distillation. The method involves describing the system in terms of new composition coordinates which represent the reactive system in a lower dimensional composition space. The justification for these new variables is that when equilibrium chemical reactions occur in a mixture, the

Sophie Ung; Michael F. Doherty

1995-01-01

106

Exact stochastic simulation of coupled chemical reactions with delays  

Microsoft Academic Search

Gillespie's exact stochastic simulation algorithm (SSA) [J. Phys. Chem. 81, 2350 (1977)] has been widely used to simulate the stochastic dynamics of chemically reacting systems. In this algorithm, it is assumed that all reactions occur instantly. While this is true in many cases, it is also possible that some chemical reactions, such as gene transcription and translation in living cells,

Xiaodong Cai

2007-01-01

107

Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction.  

ERIC Educational Resources Information Center

|Describes a dramatic chemical demonstration in which chemicals that are black and white combine to produce a colorless liquid. Reactants include tincture of iodine, bleach, white vinegar, Epsom salt, vitamin C tablets, and liquid laundry starch. (DDR)|

Wright, Stephen W.

2002-01-01

108

Heat-of-Reaction Chemical Heat Pumps.  

National Technical Information Service (NTIS)

Chemical heat pumps are mechanically driven heat pumps with working fluids that undergo chemical changes or are heat-driven heat pumps in which either the driver (heat engine) or heat pump utilizes a reactive working fluid. As such, chemical heat pumps ca...

C. Bliem L. Kirol

1988-01-01

109

Visualization of electronic properties of molecules in chemical reactions  

Microsoft Academic Search

Modern computational methods allow for the tracking of entire chemical reactions, ranging from initial reactants, through transition states, and to the final products. They also permit the computation of a variety of properties that can change as the reaction proceeds from start to finish. Visualization of these reactions is often difficult and usually limited to static displays of specific steps

Susanna Wei; George R. Famini

1995-01-01

110

LIGAND: database of chemical compounds and reactions in biological pathways  

Microsoft Academic Search

LIGAND is a composite database comprising three sections: COMPOUND for the information about metabolites and other chemical compounds, REACTION for the collection of substrate-product relations representing metabolic and other reactions, and ENZYME for the information about enzyme molecules. The current release (as of September 7, 2001) includes 7298 compounds, 5166 reactions and 3829 enzymes. In addition to the keyword search

Susumu Goto; Yasushi Okuno; Masahiro Hattori; Takaaki Nishioka; Minoru Kanehisa

2002-01-01

111

Quantum control of chemical reaction dynamics in a classical way  

Microsoft Academic Search

A simplified approach to quantum control of chemical reaction dynamics based on a classical, local control theory was developed. The amplitude of the control pulse is proportional to the linear momentum of the reaction system within the dipole approximation for the system-radiation field interaction. The kinetic energy of the system is the controlling parameter. That is, the reaction is controlled

Hiroaki Umeda; Yuichi Fujimura

2000-01-01

112

Droplet heat transfer and chemical reactions during direct containment heating  

SciTech Connect

A simplified model of heat transfer and chemical reaction has been adapted to evaluate the expected behavior of droplets containing unreacted Zircaloy and stainless steel moving through the containment atmosphere during postulated accidents involving direct containment heating. The model includes internal and external diffusive resistances to reaction. The results indicate that reactions will be incomplete for many conditions characteristic of direct containment heating sequences.

Baker, L. Jr.

1986-01-01

113

Chemical reactions driven by concentrated solar energy  

Microsoft Academic Search

Solar energy can be used for driving endothermic reactions, either photochemically or thermally. The fraction of the solar spectrum that can be photochemically active is quite small. Therefore, it is desirable to be able to combine photochemical and thermal processes in order to increase the overall efficiency. Two thermally driven reactions are being studied: oil shale gasification and methane reforming.

Moshe Levy

1991-01-01

114

The Activated Complex in Chemical Reactions  

Microsoft Academic Search

The calculation of absolute reaction rates is formulated in terms of quantities which are available from the potential surfaces which can be constructed at the present time. The probability of the activated state is calculated using ordinary statistical mechanics. This probability multiplied by the rate of decomposition gives the specific rate of reaction. The occurrence of quantized vibrations in the

Henry Eyring

1935-01-01

115

Organic chemical reactions in supercritical water  

Microsoft Academic Search

Water near or above its critical point (374 C, 218 atm) is attracting increased attention as a medium for organic chemistry. Most of this new attention is driven by the search for more green or environmentally benign chemical processes. Using near-critical or supercritical water (SCW) instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution

Phillip E. Savage

1999-01-01

116

FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

117

The Mystery Reaction: A Lesson on Chemical Reactions  

NSDL National Science Digital Library

This teaching resource was developed by a K-12 science teacher in the American Physiologycal Society's 2006 Frontiers in Physiology Program. For more information on this program, please visit www.frontiersinphys.org. The purpose of this lesson is to design an investigation and conduct an experiment that will allow students to explore the differences between physical and chemical changes. In this investigation, they are given the opportunity to develop a list of evidence for determining whether or not a chemical change has occurred.

Tonya Williams (Kelly Miller Middle School)

2006-08-01

118

Stretching the bonds of chemical reactions  

NASA Astrophysics Data System (ADS)

The effects of reagent stretch-excitation on the gas-phase Cl+CH 4 ? HCl+CH3 reaction are examined experimentally using a photoinitiated reaction technique in which the reagents are prepared by direct infrared absorption or stimulated Raman pumping and the products are state-selectively ionized and detected in a time-of-flight mass spectrometer. Our measurements indicate that the rovibrational distributions and state-selected differential cross sections of the HCl and CH3 products from the symmetric and antisymmetric stretch excited reactions are indistinguishable. This result suggests that the mechanisms of these nearly isoenergetic vibrationally excited reactions are similar, despite theoretical and experimental measurements that suggest the symmetric stretch enhances the reaction rate more than the antisymmetric stretch. Furthermore, we have demonstrated mode- and bond-selectivity in the Cl+CH2D2 reaction. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D 2 prepared in a local mode containing two quanta in one C-H oscillator |2000>- or in a local mode containing one quantum each in two C-H oscillators |1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction. Our results indicate that reagent stretch-excitation enhances the reaction rate by localizing energy along the reaction coordinate, thereby widening the cone of acceptance and allowing reactive collisions at high impact parameter. The chlorine atom appears to react with a single C-H oscillator, while the methyl radical is largely a spectator throughout the course of the reaction. Moreover, our results are consistent with a model in which the impact parameter governs the angular distributions of the product.

Bechtel, Hans A.

119

Developing Secondary Students' Conceptions of Chemical Reactions: The Introduction of Chemical Equilibrium.  

ERIC Educational Resources Information Center

|Describes an empirical study concerning the introduction of the concept of chemical equilibrium in chemistry classrooms in a way which challenges students' initial conceptions of chemical reactions. Contains 23 references. (DDR)|

Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico; Dekkers, Hetty

1998-01-01

120

Chemical Reactions in the Helium Impurities Loop.  

National Technical Information Service (NTIS)

The Helium Impurities Loop (HIL) at Brookhaven National Laboratory has been run to study reactions between the three metals and the four major helium oxidation and reduction and on carburization of the metals. Preliminary work on hydrogen diffusion throug...

L. G. Epel D. G. Schweitzer

1978-01-01

121

Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory  

Microsoft Academic Search

The purpose of this article is to discuss two colorful reactions not widely used by chemical educators in high schools or college chemistry laboratories: The synthesis of zinc iodide from its elements, zinc and iodine, and the subsequent decomposition of zinc iodide back into its elements. These reactions are important for chemistry teachers to know about because they can be

Stephen Demeo

1995-01-01

122

29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH FORMER GENERAL OFFICE BUILDING IN BACKGROUND. - U.S. Steel Duquesne Works, Fuel & Utilities Plant, Along Monongahela River, Duquesne, Allegheny County, PA

123

Design and development of chemical ontologies for reaction representation.  

PubMed

This paper describes the development of chemical ontologies applied to the representation of organic chemical reactions. The ontologies are built using the methodology known as methontology. The hierarchically structured set of terms describing the subdomains, namely, organic reactions, organic compounds, and reagents, are constructed into individual ontologies. The ontologies consist of about 200 concepts and around 125 individuals. A set of binary relations is defined in order to integrate the ontologies with applications. The ontologies are implemented as an XML application with a set of vocabulary describing the domain knowledge. This paper also features an easy-to-use chemical ontological support system (COSS) intended to represent organic chemical reactions automatically. As a model application, the automatic representation of aliphatic nucleophilic substitution reactions is demonstrated using COSS. The paper also describes a keyword-based search system whose functionality is backed with COSS. PMID:17125179

Sankar, Punnaivanam; Aghila, Gnanasekaran

124

Chemical reactions during the optical breakdown of dielectric coatings  

NASA Astrophysics Data System (ADS)

It is shown that the destruction of many types of dielectric coatings is connected with chemical reactions (including solid-phase reactions) initiated by laser radiation. Thermodynamic calculations, and microluminescence and microchemical analyses show that coatings containing ZnS, and oxides of zirconium, hafnium, and titanium in combination with SiO2 are chemically unstable. Absorbing microdefects, whose appearance is determined by chemical reactions on catalytically active centers, facilitate the heating of coatings to the reaction-initiation temperature. The reaction rate depends on the radiation power density, the number of active centers in the coating (lattice defects, dislocations, inclusions, etc.), and the reagent diffusion rate. It is concluded that, in order to assure the high radiation resistance of dielectric coatings, it is necessary to use materials of high thermodynamic stability under laser radiation.

Artemev, V. A.; Bonch-Bruevich, A. M.; Chernaia, Iu. I.

1980-10-01

125

CHEMICAL REACTIONS SIMULATED BY GROUND-WATER-QUALITY MODELS.  

USGS Publications Warehouse

Recent literature concerning the modeling of chemical reactions during transport in ground water is examined with emphasis on sorption reactions. The theory of transport and reactions in porous media has been well documented. Numerous equations have been developed from this theory, to provide both continuous and sequential or multistep models, with the water phase considered for both mobile and immobile phases. Chemical reactions can be either equilibrium or non-equilibrium, and can be quantified in linear or non-linear mathematical forms. Non-equilibrium reactions can be separated into kinetic and diffusional rate-limiting mechanisms. Solutions to the equations are available by either analytical expressions or numerical techniques. Saturated and unsaturated batch, column, and field studies are discussed with one-dimensional, laboratory-column experiments predominating. A summary table is presented that references the various kinds of models studied and their applications in predicting chemical concentrations in ground waters.

Grove, David, B.; Stollenwerk, Kenneth, G.

1987-01-01

126

SIMPLIFICATION OF CHEMICAL REACTION SYSTEMS BY TIMESCALE ANALYSIS  

Microsoft Academic Search

In this article, we present a model order reduction method based on time-scale analysis for chemical reaction systems. The method can be applied to any reaction system exhibiting multiple time scales and described by the set or differential equations dc\\/dl = f(c), where c (dimension n) is the vector of chemical species and f is the operator describing the kinetics.

MILES S. OKINO; MICHAEL L. MAVROVOUNIOTIS

1999-01-01

127

Mechanics driven Chemical Reactions in Structural Energetic Materials  

Microsoft Academic Search

Fundamental mechanisms that are responsible for shock-initiation of chemical reactions, are dominated by non-equilibrium processes including changes in reactant particle configurations caused by plastic deformation or by fracture, mixing of constituents in and around the voids, and rapid increases in temperature from mechanical work. Mechanics driven chemical reactions occur in structural energetic mixtures, during the high-pressure shock state in time

Vindhya Narayanan; Derek Redding; Sathya Hanagud

2007-01-01

128

Drying with Chemical Reaction in Cocoa Beans  

Microsoft Academic Search

Desirable flavor qualities of cocoa are dependent on how the cocoa beans are fermented, dried, and roasted. During fermentation and drying, polyphenols such as leucocyanidin and apecatechin are oxidized by polyphenols oxidase to form o-quinone, which later react nonenzymatically with a hydroquinone in a condensation reaction to form browning products and moisture. The objective of this article is to model

Wan Ramli Wan Daud; Meor Zainal Meor Talib; Tin Mar Kyi

2007-01-01

129

Anatomy of an Elementary Chemical Reaction  

Microsoft Academic Search

The alchemists of old sought the knowledge to transform one material to another-for example, base metals into gold-as a path to the elixir of life. As chemists have concerned themselves with the transformation from compound to compound, so they have become involved in trying to uncover the structures of molecules and the pathways that reactions follow. Classically, the study of

Andrew J. Alexander; Richard N. Zare

1998-01-01

130

Laser cutting with chemical reaction assist.  

National Technical Information Service (NTIS)

This invention is comprised of a method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. oxygen is supplied to the laser focus point...

D. J. Gettemy

1991-01-01

131

Memory Switches in Chemical Reaction Space  

Microsoft Academic Search

Just as complex electronic circuits are built from simple Boolean gates, diverse biological functions, including signal transduction, differentiation, and stress response, frequently use biochemical switches as a functional module. A relatively small number of such switches have been described in the literature, and these exhibit considerable diversity in chemical topology. We asked if biochemical switches are indeed rare and if

Naren Ramakrishnan; Upinder S. Bhalla

2008-01-01

132

Chemical pathways in ultracold reactions of SrF molecules  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of the chemical reaction SrF + SrF ? products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF ? Sr2 + F2 is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF ? SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule “handing off” a fluorine atom to the other molecule.

Meyer, Edmund R.; Bohn, John L.

2011-03-01

133

Chemical pathways in ultracold reactions of SrF molecules  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of the chemical reaction SrF + SrF -> products, focusing on reactions at ultralow temperatures. We find that bond swapping, SrF + SrF -> Sr2 + F2, is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF -> SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless, and proceeds by one SrF molecule ``handing off'' a fluorine atom to the other molecule.

Meyer, Edmund; Bohn, John

2011-06-01

134

Screening in Low Energy Nuclear Reactions of Importance to Astrophysics  

NASA Astrophysics Data System (ADS)

Recent experiments in the LUNAR (Laboratory for Underground Nuclear Astrophysics) project have shown anonymously high electron screening may occur during acceleration driven low energy (<400 kV) ion bombardment of solid targets [1]. These effects become particularly important for E/ Ue < 100 (here E= ion energy and Ue = electron-screening potential energy). Thus these effects become significant for the understanding of reactions involved in nucleosynthesis of the elements and the interpretation of astrophysical data [1]. Another example of the behavior is the surprising threshold behavior near 18 keV for deuterons stopping in 3He gas at energies below the Bragg peak [2]. As pointed out in ref [1], the theoretical explanation for these effects is still under debate. Several researchers have proposed variations of the Trojan Horse Method (THM) to explain these effects [3]. In this paper, we propose an alternate mechanism associated with electron charge accumulation around the target atoms arising from the solid-state structure of the host. This concept will be explained in terms of density functional calculations of charge density profiles in a target undergoing ion dynamic effects [4]. REFERENCES [1] F. Strieder, et al., Naturwissenschaften (2000)88:461-467 [2] A. Formicola, et al., (2000) Eur Phys J. A 8:443-446 [3] S. Typel and H H Wolter, (2000) Few-Body System 29:75-93 [4] G. Miley and H. Hora, (2000) Nuclear Reactions in Solids, APS mtg. Lansing, MI [5] G. Miley, A. Lipson, N. Luo, and H. Hora, (2003) IEEE NSS/MIC Conf., Portland, OR

Miley, George H.; Hora, Heinz; Luo, Nie

2004-05-01

135

Using Large Glass Cylinders To Demonstrate Chemical Reactions  

Microsoft Academic Search

This article describes a simple laboratory experiment that aims at pedagogic as well as aesthetic aspects of chemical reactions. In a 0.5- or 1-liter glass cylinder almost completely filled with water, a slow precipitation reaction involving two soluble salts is made to occur by adding a sample of one salt directly to the water and then placing some of the

Wobbe de Vos

1999-01-01

136

Chemical reactions on solid surfaces of astrophysical interest  

Microsoft Academic Search

Observed abundances of chemical species in interstellar clouds can be explained in most cases by reaction schemes involving only species in the gas phase. There is however clear evidence that reactions occurring on the surface of dust grains, helping the formation of key molecules, play a fundamental role into shaping the universe as we see it today. In this chapter

Ofer Biham; Valerio Pirronello; Gianfranco Vidali

2003-01-01

137

Two-photon induced chemical reactions in liquids  

SciTech Connect

A two-photon absorption process has been used for the first time to produce significant quantities of reaction products between halogen containing organic compounds and silver containing inorganic compounds in the condensed phase. The mechanisms for these chemical reactions were also studied and confirmed by two-photon absorption spectra and optoaccoustic methods.

Chen, C.H.; McCann, M.P. (Chemical Physics Section, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6378 (US))

1989-10-20

138

Brownian dynamics simulation of a chemical reaction in solution  

Microsoft Academic Search

We present a study, using the brownian dynamics simulation technique, of a simple model of a chemical reaction in solution. The model consists of the transfer of a particle between two substrate species in a reaction complex which interacts with its surroundings through frictional effects and random force terms. We pay particular attention to the regime in which both the

M. P. Allen

1980-01-01

139

Evaluated Chemical Kinetic Rate Constants for Various Gas Phase Reactions  

Microsoft Academic Search

The available information, up to mid-1972, for the rate constants of a series of gas phase chemical reactions has been evaluated critically. For each reaction, relevant thermodynamic data are presented and values for the equilibrium constant expressed in mathematical form. Kinetic data are presented in tabular and graphical form together with a discussion of the pertinent details. Recommended rate constant

Keith Schofield

1973-01-01

140

Incorporation of Chemical Reactions into Building-scale Flow  

Microsoft Academic Search

Many hazardous atmospheric releases involve chemical reactions that occur within a few kilometers of the source. Reactions with commonly occurring atmospheric compounds such as the OH radical, can transform and potentially neutralize original release compounds. Especially in these cases, accurately resolving flow around nearby structures and over surrounding topography can be critical to correctly predicting material dispersion, and thus, the

T D Humphreys; T M Jayaweera; R L Lee

2003-01-01

141

Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks  

ERIC Educational Resources Information Center

|Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to…

Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

2011-01-01

142

Influence of trace impurities on chemical reaction hazards  

Microsoft Academic Search

The influence of trace impurities is frequently mentioned as a possible or probable cause of accidents in the chemical industry. In process conditions where there is a potential for a fast exothermic decomposition or polymerisation reaction, the contamination of pure chemicals by trace impurities may cause problems. Typical examples of this situation are described concerning the processing of organic nitrocompounds

J. L. Gustin

2002-01-01

143

Results of the 2010 Survey on Teaching Chemical Reaction Engineering  

ERIC Educational Resources Information Center

A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the…

Silverstein, David L.; Vigeant, Margot A. S.

2012-01-01

144

Results of the 2010 Survey on Teaching Chemical Reaction Engineering  

ERIC Educational Resources Information Center

|A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the…

Silverstein, David L.; Vigeant, Margot A. S.

2012-01-01

145

Symmetry numbers and chemical reaction rates  

Microsoft Academic Search

This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them\\u000a to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational\\u000a symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i)\\u000a if the reaction

Antonio Fernández-Ramos; Benjamin A. Ellingson; Rubén Meana-Pañeda; Jorge M. C. Marques; Donald G. Truhlar

2007-01-01

146

Cu-free click cycloaddition reactions in chemical biology†  

PubMed Central

Bioorthogonal chemical reactions are paving the way for new innovations in biology. These reactions possess extreme selectivity and biocompatibility, such that their participating reagents can form covalent bonds within richly functionalized biological systems—in some cases, living organisms. This tutorial review will summarize the history of this emerging field, as well as recent progress in the development and application of bioorthogonal copper-free click cycloaddition reactions.

Jewett, John C.

2010-01-01

147

LIGAND: Database of Chemical Compounds and Reactions in Biological Pathways  

NSDL National Science Digital Library

The Institute for Chemical Research at Kyoto University provides this frequently updated and well-documented database of enzyme reactions. With more than 9,300 entries, the LIGAND Chemical Database includes over 3,700 entries for enzymes (the Enzyme Reaction Database) and 5,600 entries for compounds (Chemical Compound Database). The database is searchable by keyword using DBGET (which supports numerous other databases and gene catalogs as well) and is accompanied by clear instructions. The LIGAND database, updated weekly, may be downloaded via anonymous FTP.

148

Chemical reactions driven by concentrated solar energy  

NASA Astrophysics Data System (ADS)

Solar energy can be used for driving endothermic reactions, either photochemically or thermally. The fraction of the solar spectrum that can be photochemically active is quite small. Therefore, it is desirable to be able to combine photochemical and thermal processes in order to increase the overall efficiency. Two thermally driven reactions are being studied: oil shale gasification and methane reforming. In both cases, the major part of the work was done in opaque metal reactors where photochemical reactions cannot take place. We then proceeded working in transparent quartz reactors. The results are preliminary, but they seem to indicate that there may be some photochemical enhancement. The experimental solar facilities used for this work include the 30 kW Schaeffer Solar Furnace and the 3 MW Solar Central Receiver in operation at the Weizmann Institute. The furnace consists of a 96 sq. m flat heliostat, that follows the sun by computer control. It reflects the solar radiation onto a spherical concentrator, 7.3 m in diameter, with a rim angle of 65 degrees. The furnace was characterized by radiometric and calorimetric measurements to show a solar concentration ratio of over 10,000 suns. The central receiver consists of 64 concave heliostats, 54 sq. m each, arranged in a north field and facing a 52 m high tower. The tower has five target levels that can be used simultaneously. The experiments with the shale gasification were carried out at the lowest level, 20 m above ground, which has the lowest solar efficiency and is assigned for low power experiments. We used secondary concentrators to boost the solar flux.

Levy, Moshe

149

Exact stochastic simulation of coupled chemical reactions with delays  

NASA Astrophysics Data System (ADS)

Gillespie's exact stochastic simulation algorithm (SSA) [J. Phys. Chem. 81, 2350 (1977)] has been widely used to simulate the stochastic dynamics of chemically reacting systems. In this algorithm, it is assumed that all reactions occur instantly. While this is true in many cases, it is also possible that some chemical reactions, such as gene transcription and translation in living cells, take certain time to finish after they are initiated. Thus, the product of such reactions will emerge after certain delays. Apparently, Gillespie's SSA is not an exact algorithm for chemical reaction systems with delays. In this paper, the author develops an exact SSA for chemical reaction systems with delays, based upon the same fundamental premise of stochastic kinetics used by Gillespie in the development of his SSA. He then shows that an algorithm modified from Gillespie's SSA by Barrio et al. [PLOS Comput. Biol. 2, 1017 (2006)] is also an exact SSA for chemical reaction systems with delays, but it needs to generate more random variables than the author's algorithm.

Cai, Xiaodong

2007-03-01

150

A robustness screen for the rapid assessment of chemical reactions.  

PubMed

In contrast to the rapidity with which scientific information is published, the application of new knowledge often remains slow, and we believe this to be particularly true of newly developed synthetic organic chemistry methodology. Consequently, methods to assess and identify robust chemical reactions are desirable, and would directly facilitate the application of newly reported synthetic methodology to complex synthetic problems. Here, we describe a simple process for assessing the likely scope and limitations of a chemical reaction beyond the idealized reaction conditions initially reported. Using simple methods and common analytical techniques we demonstrate a rapid assessment of an established chemical reaction, and also propose a simplified analysis that may be reported alongside new synthetic methodology. PMID:23787750

Collins, Karl D; Glorius, Frank

2013-06-09

151

The effect of carbon nanotubes on chiral chemical reactions  

NASA Astrophysics Data System (ADS)

The intrinsic helicity of carbon nanotubes influences the formation of chiral molecules in chemical reactions. A racemic mixture of P and M enantiomers of nanotubes affects the enantiomeric excess of the products of the autocatalytic Soai reaction proportional to the amount of nanotubes added in the reaction mixture. An intermediate complex formed between the nanotube and the organometallic reagent is essential and explains the observed correlation between the enantiomeric distribution of products and the curvature of the carbon nanostructure. This Letter establishes a key mechanism for harnessing the helicity of nanoscale carbon surfaces for preparative organic reactions.

Rance, Graham A.; Miners, Scott A.; Chamberlain, Thomas W.; Khlobystov, Andrei N.

2013-02-01

152

Acceleration of chemical reactions within a shock wave front  

NASA Astrophysics Data System (ADS)

The aim of the present numerical study was to illustrate the possible influence of translational nonequilibrium in the front of a shock wave on the rate of the threshold chemical reaction. The Monte Carlo method of nonstationary statistical simulation with variable weighting factors was used. Gas mixtures which contained, ahead of the front, two chemically interacting small additives A1, A2 and an inert light main component were considered. A chemical reaction of the additives started in the front of a shock wave and led to formation of two new low-concentration components A3 and A4. It was shown that for the ratio of molecular number densities of the additives A1, A2 and an inert component A5 of 1:10:200 and for the molecular mass ratio of components A1, A2, A3, A4, A5 of 34.5:8:38.5:4:1 the value of the direct reaction rate obtained in the front exceeds its equilibrium value behind the wave by more than 100 times. As a result, the reaction occurs more intensively in the zone of translational nonequilibrium. It was also shown that for the cases of an exothermic reaction and a weak endothermic reaction, a small amount of the light reaction product has the velocity of the shock wave and is carried by the front.

Kulikov, S. V.

153

Mining chemical reactions using neighborhood behavior and condensed graphs of reactions approaches.  

PubMed

This work addresses the problem of similarity search and classification of chemical reactions using Neighborhood Behavior (NB) and Condensed Graphs of Reaction (CGR) approaches. The CGR formalism represents chemical reactions as a classical molecular graph with dynamic bonds, enabling descriptor calculations on this graph. Different types of the ISIDA fragment descriptors generated for CGRs in combination with two metrics--Tanimoto and Euclidean--were considered as chemical spaces, to serve for reaction dissimilarity scoring. The NB method has been used to select an optimal combination of descriptors which distinguish different types of chemical reactions in a database containing 8544 reactions of 9 classes. Relevance of NB analysis has been validated in generic (multiclass) similarity search and in clustering with Self-Organizing Maps (SOM). NB-compliant sets of descriptors were shown to display enhanced mapping propensities, allowing the construction of better Self-Organizing Maps and similarity searches (NB and classical similarity search criteria--AUC ROC--correlate at a level of 0.7). The analysis of the SOM clusters proved chemically meaningful CGR substructures representing specific reaction signatures. PMID:22894688

de Luca, Aurélie; Horvath, Dragos; Marcou, Gilles; Solov'ev, Vitaly; Varnek, Alexandre

2012-09-04

154

STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis  

NASA Astrophysics Data System (ADS)

The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

Hla, Saw-Wai; Rieder, Karl-Heinz

2003-10-01

155

Asymmetric chemical reactions by polarized quantum beams  

NASA Astrophysics Data System (ADS)

One of the most attractive hypothesis for the origin of homochirality in terrestrial bio-organic compounds (L-amino acid and D-sugar dominant) is nominated as "Cosmic Scenario"; a chiral impulse from asymmetric excitation sources in space triggered asymmetric reactions on the surfaces of such space materials as meteorites or interstellar dusts prior to the existence of terrestrial life. 1) Effective asymmetric excitation sources in space are proposed as polarized quantum beams, such as circularly polarized light and spin polarized electrons. Circularly polarized light is emitted as synchrotron radiation from tightly captured electrons by intense magnetic field around neutron stars. In this case, either left-or right-handed polarized light can be observed depending on the direction of observation. On the other hand, spin polarized electrons is emitted as beta-ray in beta decay from radioactive nuclei or neutron fireballs in supernova explosion. 2) The spin of beta-ray electrons is longitudinally polarized due to parity non-conservation in the weak interaction. The helicity (the the projection of the spin onto the direction of kinetic momentum) of beta-ray electrons is universally negative (left-handed). For the purpose of verifying the asymmetric structure emergence in bio-organic compounds by polarized quantum beams, we are now carrying out laboratory simulations using circularly polarized light from synchrotron radiation facility or spin polarized electron beam from beta-ray radiation source. 3,4) The target samples are solid film or aqueous solution of racemic amino acids. 1) K.Kobayashi, K.Kaneko, J.Takahashi, Y.Takano, in Astrobiology: from simple molecules to primitive life; Ed. V.Basiuk; American Scientific Publisher: Valencia, 2008. 2) G.A.Gusev, T.Saito, V.A.Tsarev, A.V.Uryson, Origins Life Evol. Biosphere. 37, 259 (2007). 3) J.Takahashi, H.Shinojima, M.Seyama, Y.Ueno, T.Kaneko, K.Kobayashi, H.Mita, M.Adachi, M.Hosaka, M.Katoh, Int. J. Mol. Sci. 10, 3044 (2009). 4) V.I.Burkov, L.A.Goncharova, G.A.Gusev, H.Hashimoto, F.Kaneko, T.Kaneko, K. Kobayashi, H.Mita, E.V.Moiseenko, T.Ogawa, N.G.Poluhina, T.Saito, S.Shima, J.Takahashi, M.Tanaka, Y.Tao, V.A.Tsarev, J.Xu, H.Yabuta, K.Yagi-Watanabe, H.Yan, G.Zhang, Origins Life Evol. Biosphere, 39 295 (2009).

Takahashi, Jun-Ichi; Kobayashi, Kensei

156

The Electronic Flux in Chemical Reactions. Insights on the Mechanism of the Maillard Reaction  

NASA Astrophysics Data System (ADS)

The electronic transfer that occurs during a chemical process is analysed in term of a new concept, the electronic flux, that allows characterizing the regions along the reaction coordinate where electron transfer is actually taking place. The electron flux is quantified through the variation of the electronic chemical potential with respect to the reaction coordinate and is used, together with the reaction force, to shed light on reaction mechanism of the Schiff base formation in the Maillard reaction. By partitioning the reaction coordinate in regions in which different process might be taking place, electronic reordering associated to polarization and transfer has been identified and found to be localized at specific transition state regions where most bond forming and breaking occur.

Flores, Patricio; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Silva, Eduardo; Toro-Labbé, Alejandro

2007-11-01

157

Multiple Equilibria in Complex Chemical Reaction Networks: II. The Species-Reaction Graph  

Microsoft Academic Search

For mass action kinetics, the capacity for multiple equilibria in an isothermal homo- geneous continuous ?ow stirred tank reactor is determined by the structure of the underlying network of chemical reactions. We suggest a new graph-theoretical method for discriminating between com- plex reaction networks that can admit multiple equilibria and those that cannot. In particular, we associate with each network

Gheorghe Craciun; Martin Feinberg

2006-01-01

158

Simulation of chemical reaction equilibria by the reaction ensemble Monte Carlo method: a review†  

Microsoft Academic Search

Understanding and predicting the equilibrium behaviour of chemically reacting systems in highly non-ideal environments is critical to many fields of science and technology, including solvation, nanoporous materials, catalyst design, combustion and propulsion science, shock physics and many more. A method with recent success in predicting the equilibrium behaviour of reactions under non-ideal conditions is the reaction ensemble Monte Carlo method

C. Heath Turner; John K. Brennan; Martin Lísal; William R. Smith; J. Karl Johnson; Keith E. Gubbins

2008-01-01

159

Shock-induced chemical reactions and synthesis of binary compounds  

SciTech Connect

The results of an experimental program on shock-induced chemical reactions and synthesis of binary compounds are presented. Binary powder mixture systems that are investigated include: (1) intermetallic forming compounds (e.g., Ni--Al, Ni--Si, Nb--Si, etc.) associated with large negative heats of reaction; and (2) isomorphous (e.g., Ni--Cu) and fully immiscible (e.g., Nb--Cu) systems associated with zero (or positive) heat of reaction. The extent of shock induced chemical reactions and the type of shock synthesized compounds formed in these systems are observed to be dependent on (i) shock-loading condition, (ii) the relative volumetric distribution of the mixture constituents, and (iii) differences in respective material properties which affect relative particle flow. 5 refs., 9 figs.

Thadhani, N.N.; Advani, A.; Song, I.; Dunbar, E.; Grebe, A. (New Mexico Inst. of Mining and Technology, Socorro, NM (USA). Center for Explosives Technology Research); Graham, R.A. (Sandia National Labs., Albuquerque, NM (USA))

1990-01-01

160

Kramers problem for nonequilibrium current-induced chemical reactions.  

PubMed

We discuss the use of tunneling electron current to control and catalyze chemical reactions. Assuming the separation of time scales for electronic and nuclear dynamics we employ Langevin equation for a reaction coordinate. The Langevin equation contains nonconservative current-induced forces and gives nonequilibrium, effective potential energy surface for current-carrying molecular systems. The current-induced forces are computed via Keldysh nonequilibrium Green's functions. Once a nonequilibrium, current-depended potential energy surface is defined, the chemical reaction is modeled as an escape of a Brownian particle from the potential well. We demonstrate that the barrier between the reactant and the product states can be controlled by the bias voltage. When the molecule is asymmetrically coupled to the electrodes, the reaction can be catalyzed or stopped depending on the polarity of the tunneling current. PMID:21861578

Dzhioev, Alan A; Kosov, D S

2011-08-21

161

Machine learning of chemical reactivity from databases of organic reactions  

Microsoft Academic Search

Databases of chemical reactions contain knowledge about the reactivity of specific reagents. Although information is in general\\u000a only explicitly available for compounds reported to react, it is possible to derive information about substructures that do\\u000a not react in the reported reactions. Both types of information (positive and negative) can be used to train machine learning\\u000a techniques to predict if a

Gonçalo V. S. M. Carrera; Sunil Gupta; João Aires-de-Sousa

2009-01-01

162

Method and apparatus for controlling gas evolution from chemical reactions  

DOEpatents

The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846.

Skorpik, James R. (Kennewick, WA); Dodson, Michael G. (Richland, WA)

1999-01-01

163

Method and apparatus for controlling gas evolution from chemical reactions  

DOEpatents

The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846. 8 figs.

Skorpik, J.R.; Dodson, M.G.

1999-05-25

164

The Chemical Reaction Model Recent Developments and Prospects  

Microsoft Academic Search

In 2001, we gave a survey of more than fifteen years of research on the chemical paradigm which had been a source of inspiration\\u000a in many different research areas. The present article presents a digest of recent advances concerning the chemical reaction\\u000a model. We focus to a large extent on: (1) upgrading the basic model to a higher order formalism

Jean-pierre Banâtre; Pascal Fradet; Yann Radenac

2008-01-01

165

Shrinkage Dynamics of a Vesicle Induced by Chemical Reactions  

NASA Astrophysics Data System (ADS)

We study the shrinkage dynamics of a vesicle out of equilibrium. In our previous paper, we introduced a kinetic theory of a vesicle interacting with surfactant molecules. In the present paper, we extend the theory to cover more variety of chemical reactions. It is shown that the chemical kinetics change drastically the relation between the waiting time of pore formation and the radius of vesicle. Numerical simulations are carried out to confirm our analytical results.

Kaga, Masafumi; Ohta, Takao

2007-09-01

166

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds  

SciTech Connect

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic models of the three surrogates and GB are then used to predict their consumption in a perfectly stirred reactor fueled by natural gas to simulate incineration of these chemicals. Computed results indicate that DIMP is the only one of these surrogates that adequately describes combustion of GB under comparable conditions. The kinetic pathways responsible for these differences in reactivity are identified and discussed. The most important reaction in GB and DIMP that makes them more reactive than TMP or DMMP is found to be a six-center molecular elimination reaction producing propene.

Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K

2001-12-13

167

INVESTIGATION OF IMPORTANT HYDROXYL RADICAL REACTIONS IN THE PERTURBED TROPOSPHERE  

EPA Science Inventory

The flash-photolysis resonance fluorescence technique was used to study the reaction kinetics of hydroxyl radicals with ten aromatic and six olefinic hydrocarbons at 298 K and several diluent gas pressures. The aromatic compounds that were studied include benzene, toluene, ethylb...

168

Gas-Phase Reactions of Halogen Species of Atmospheric Importance.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. A low-pressure discharge-flow technique, with various optical detection methods, has been used to determine bimolecular rate coefficients for a number of reactions in the gas-phase between OH radicals and organic halogen -containing molecules and between NO_3 radicals and the iodine species I_2 and I. These experiments have shown that: (i) the reaction of methyl iodide with OH accounts for approximately 2% of the removal of CH_3I from the troposphere as compared with photolysis; (ii) abstraction of I-atoms from a C-I bond by OH is probable in the gas -phase; (iii) the halogen-containing anaesthetic substances halothane CF_3CCl BrH, enflurane CF_2HOCF _2CFClH, isoflurane CF_2HOCClHCF _3 and sevoflurane (CF_3) _2CHOCFH_2 have significantly shorter tropospheric lifetimes than the fully halogenated CFCs and halons because of reaction with the OH radical and are thus unlikely to be transported up to the stratosphere where they could contribute to the depletion of ozone. Data obtained for reactions between OH and some 'CFC alternatives' along with measurements of the integrated absorption cross -sections of the compounds in the spectral region 800-1200 cm^{-1} were used to calculate ozone depletion potentials (ODP) and greenhouse warming potentials relative to CFCl_3 for each compound. The study of the reactions between OH and CF_3CFBrH and CF _2BrH was used to provide a useful first estimate of the environmental acceptability of these compounds in the context of their possible use as replacements for the conventional CFCs. A method was developed to provide a first estimate of the ODP of a halogenated alkane without use of a complicated (and expensive) computer modeling scheme. A reaction between molecular iodine and the nitrate radical in the gas-phase was discovered and the kinetics of this reaction have been studied. No temperature or pressure dependence was observed for the rate of reaction, the rate constant of which was found to be (1.5 +/- 0.5) times 10 ^{-12}cm^{ -3}molecule^{-1}s ^{-1}. The reaction between I and NO_3 was found to occur at a rate of about 60% of the hard-sphere collision frequency for the two species. The rate constant for reaction between I and NO_3 was found to be (4.5 +/- 1.9) times 10^{-10}cm^3 molecule^{-1}s ^{-1}. An upper limit for the heat of formation of IONO_2 of (21 +/- 3) kJmol^ {-1} was also derived. (Abstract shortened by UMI.).

Heard, Anne C.

169

Reduction of chemical reaction networks through delay distributions  

NASA Astrophysics Data System (ADS)

Accurate modelling and simulation of dynamic cellular events require two main ingredients: an adequate description of key chemical reactions and simulation of such chemical events in reasonable time spans. Quite logically, posing the right model is a crucial step for any endeavour in Computational Biology. However, more often than not, it is the associated computational costs which actually limit our capabilities of representing complex cellular behaviour. In this paper, we propose a methodology aimed at representing chains of chemical reactions by much simpler, reduced models. The abridgement is achieved by generation of model-specific delay distribution functions, consecutively fed to a delay stochastic simulation algorithm. We show how such delay distributions can be analytically described whenever the system is solely composed of consecutive first-order reactions, with or without additional ``backward'' bypass reactions, yielding an exact reduction. For models including other types of monomolecular reactions (constitutive synthesis, degradation, or ``forward'' bypass reactions), we discuss why one must adopt a numerical approach for its accurate stochastic representation, and propose two alternatives for this. In these cases, the accuracy depends on the respective numerical sample size. Our model reduction methodology yields significantly lower computational costs while retaining accuracy. Quite naturally, computational costs increase alongside network size and separation of time scales. Thus, we expect our model reduction methodologies to significantly decrease computational costs in these instances. We anticipate the use of delays in model reduction will greatly alleviate some of the current restrictions in simulating large sets of chemical reactions, largely applicable in pharmaceutical and biological research.

Barrio, Manuel; Leier, André; Marquez-Lago, Tatiana T.

2013-03-01

170

Chemical pathways in ultracold reactions of SrF molecules  

SciTech Connect

We present a theoretical investigation of the chemical reaction SrF + SrF {yields} products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF {yields} Sr{sub 2} + F{sub 2} is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF {yields} SrF{sub 2} + Sr, and even then only singlet states of the SrF{sub 2} trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule ''handing off'' a fluorine atom to the other molecule.

Meyer, Edmund R.; Bohn, John L. [JILA, NIST, and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2011-03-15

171

Developing secondary students’ conceptions of chemical reactions: the introduction of chemical equilibrium  

Microsoft Academic Search

This article describes an empirical study concerning the introduction of the chemical equilibrium concept in chemistry classrooms in a way which challenges secondary students’ initial conceptions of chemical reactions. The objectives of this study were to identify the types of reasoning students use in this context and to develop teaching strategies which promote conceptual change in this respect. As a

Jan H. Van Driel; Wobbe De Vos; Nico Verloop; Hetty Dekkers

1998-01-01

172

Development of a chemical oxygen - iodine laser with production of atomic iodine in a chemical reaction  

SciTech Connect

The alternative method of atomic iodine generation for a chemical oxygen - iodine laser (COIL) in chemical reactions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied. (lasers)

Censky, M; Spalek, O; Jirasek, V; Kodymova, J [Institute of Physics, Czech Academy of Sciences, Prague (Czech Republic); Jakubec, I [Institute of Inorganic Chemistry, Czech Academy of Sciences, Rez (Czech Republic)

2009-11-30

173

Chemical reaction mediated self-assembly of PTCDA into nanofibers.  

PubMed

Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry. PMID:21814688

Sayyad, Arshad S; Balakrishnan, Kaushik; Ajayan, Pulickel M

2011-08-03

174

Quantum and semiclassical theories of chemical reaction rates  

SciTech Connect

A rigorous quantum mechanical theory (and a semiclassical approximation thereto) is described for calculating chemical reaction rates ``directly``, i.e., without having to solve the complete state-to-state reactive scattering problem. The approach has many vestiges of transition state theory, for which it may be thought of as the rigorous generalization.

Miller, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1995-09-01

175

Molecular Codes in Biological and Chemical Reaction Networks  

PubMed Central

Shannon’s theory of communication has been very successfully applied for the analysis of biological information. However, the theory neglects semantic and pragmatic aspects and thus cannot directly be applied to distinguish between (bio-) chemical systems able to process “meaningful” information from those that do not. Here, we present a formal method to assess a system’s semantic capacity by analyzing a reaction network’s capability to implement molecular codes. We analyzed models of chemical systems (martian atmosphere chemistry and various combustion chemistries), biochemical systems (gene expression, gene translation, and phosphorylation signaling cascades), an artificial chemistry, and random reaction networks. Our study suggests that different chemical systems posses different semantic capacities. No semantic capacity was found in the model of the martian atmosphere chemistry, the studied combustion chemistries, and highly connected random networks, i.e. with these chemistries molecular codes cannot be implemented. High semantic capacity was found in the studied biochemical systems and in random reaction networks where the number of second order reactions is twice the number of species. We conclude that our approach can be applied to evaluate the information processing capabilities of a chemical system and may thus be a useful tool to understand the origin and evolution of meaningful information, e.g. in the context of the origin of life.

Gorlich, Dennis; Dittrich, Peter

2013-01-01

176

Chemical reaction models for non-equilibrium phase transitions  

Microsoft Academic Search

Chemical model reactions are discussed the steady states of which show the phenomenon of non equilibrium phase transitions. One example shows a phase transition of second order, another one shows a phase transition of first order. If diffusion occurs in the case of first order transition, coexistence of two phases in different domains is possible. For plane boundary layers between

F. Schlögl

1972-01-01

177

Interaction between chemical reactions and mixing on various scales  

Microsoft Academic Search

The way in which reagents are mixed can have a large influence on the product distribution of a chemical reaction. This has been analysed earlier when micromixing is the limiting mixing step. Additional segregation at a larger scale has only been treated in detail when the local turbulent dispersion of a feed stream was relevant. Here additional segregation due to

S. J. Hearn

1997-01-01

178

Turbulent mixing and the selectivity of fast chemical reactions  

Microsoft Academic Search

Assuming that complete information is available about (a) the chemical reactions (mechanism, stoichiometry, thermodynamics, and kinetics) and (b) the turbulent flow field in a reactor (mean velocities and turbulence parameters), we would like to calculate directly the time evolution of the temperature and the concentrations of all species present. No general method is yet available to satisfy this goal. Starting

J. R. Bourne

1991-01-01

179

A multi-scaled approach for simulating chemical reaction systems  

Microsoft Academic Search

In this paper we give an overview of some very recent work, as well as presenting a new approach, on the stochastic simulation of multi-scaled systems involving chemical reactions. In many biological systems (such as genetic regulation and cellular dynamics) there is a mix between small numbers of key regulatory proteins, and medium and large numbers of molecules. In addition,

Kevin Burrage; Tianhai Tian; Pamela Burrage

2004-01-01

180

Chemical Reactions in Non-Aqueous Media and Molten Salts.  

National Technical Information Service (NTIS)

The symposium on Chemical Reactions in Non-aqueous Media and Molten Salts was held at the Osmania University in Hyderabad, India. Forty papers were presented of which four papers were on non-aqueous chemistry in nuclear technology, nine papers on molten s...

M. V. Ramaniah D. D. Sood V. Venugopal

1978-01-01

181

The arbitrary dynamic behavior of open chemical reaction systems  

Microsoft Academic Search

We show that if the kinetic equations describing a set of chemical reactions occurring in a one-phase closed system are only required to obey a very general set of postulates (mass conserved, concentrations nonnegative, vector fields which are continuous with continuous derivatives, existence of equilibrium, stability of equilibrium, existence of potential functions which are extremal at equilibrium, detailed balance, law

Alan S. Perelson; David Wallwork

1977-01-01

182

Stabilization of Free Radicals: its Importance in Reaction Kinetics  

Microsoft Academic Search

A PREVIOUS paper1 reported on a reaction of the radical chlorine oxide: enabling the transfer of chlorine oxide by means of addition of oxygen into the more stable chlorine trioxide and eventually, at a low temperature, into the stable chlorine hexoxide (Cl2O6). Similarly, the discussion2 of the mechanism of the decomposition of ozone sensitized or catalysed by chlorine points to

Zoltán G. Szabó

1952-01-01

183

Reaction Hamiltonian and state-to-state description of chemical reactions  

SciTech Connect

A chemical reaction is treated as a quantum transition from reactants to products. A specific reaction Hamiltonian (in second quantization formalism) is introduced. The approach leads to Franck-Condon-like factor, and adiabatic method in the framework of the nuclear motion problems. The influence of reagent vibrational state on the product energy distribution has been studied following the reaction Hamiltonian method. Two different cases (fixed available energy and fixed translational energy) are distinguished. Results for several biomolecular reactions are presented. 40 refs., 5 figs.

Ruf, B.A.; Kresin, V.Z.; Lester, W.A. Jr.

1985-08-01

184

Spectrometric Studies of Fast Reactions in Chemically Active Systems.  

National Technical Information Service (NTIS)

The report briefly summarizes research concerning the chemical compositon and stability of planetary atmospheres, - primarily oxygenic atmospheres such as that of the earth, but potentially equally important in other atmospheres such as that of Venus. The...

E. J. Bair

1970-01-01

185

Coriolis coupling and nonadiabaticity in chemical reaction dynamics.  

PubMed

The nonadiabatic quantum dynamics and Coriolis coupling effect in chemical reaction have been reviewed, with emphasis on recent progress in using the time-dependent wave packet approach to study the Coriolis coupling and nonadiabatic effects, which was done by K. L. Han and his group. Several typical chemical reactions, for example, H+D(2), F+H(2)/D(2)/HD, D(+)+H(2), O+H(2), and He+H(2)(+), have been discussed. One can find that there is a significant role of Coriolis coupling in reaction dynamics for the ion-molecule collisions of D(+)+H(2), Ne+H(2)(+), and He+H(2)(+) in both adiabatic and nonadiabatic context. PMID:20928846

Wu, Emilia L

2010-12-01

186

Mixing, chemical reaction and flow field development in ducted rockets  

SciTech Connect

Calculations have been made of the three-dimensional mixing, chemical reaction, and flow field development in a typical ducted rocket configuration. The governing partial differential equations are numerically solved by an iterative finite-difference solution procedure. The physical models include the k approx. epsilon turbulence model, one-step reaction, and mixing controlled chemical reaction rate. Radiation is neglected. The mean flow structure, fuel dispersal patterns, and temperature field are presented in detail for a base configuration with 0.058 m (2 in.) dome height, 45/sup 0/ side arm inclination, and with gaseous ethylene injected from the dome plate at an eccentric location. In addition, the influences of the geometrical parameters such as dome height, inclination of the side arms, and location of the fuel injector are studied.

Vanka, S.P.; Craig, R.R.; Stull, F.D.

1984-09-01

187

Single-molecule chemical reactions on DNA origami  

NASA Astrophysics Data System (ADS)

DNA nanotechnology and particularly DNA origami, in which long, single-stranded DNA molecules are folded into predetermined shapes, can be used to form complex self-assembled nanostructures. Although DNA itself has limited chemical, optical or electronic functionality, DNA nanostructures can serve as templates for building materials with new functional properties. Relatively large nanocomponents such as nanoparticles and biomolecules can also be integrated into DNA nanostructures and imaged. Here, we show that chemical reactions with single molecules can be performed and imaged at a local position on a DNA origami scaffold by atomic force microscopy. The high yields and chemoselectivities of successive cleavage and bond-forming reactions observed in these experiments demonstrate the feasibility of post-assembly chemical modification of DNA nanostructures and their potential use as locally addressable solid supports.

Voigt, Niels V.; Tørring, Thomas; Rotaru, Alexandru; Jacobsen, Mikkel F.; Ravnsbæk, Jens B.; Subramani, Ramesh; Mamdouh, Wael; Kjems, Jørgen; Mokhir, Andriy; Besenbacher, Flemming; Gothelf, Kurt Vesterager

2010-03-01

188

Are chemical compounds important for soybean resistance to Anticarsia gemmatalis?  

PubMed

The identification and quantification of flavonoids (rutin and genistin) present in extracts of soybean genotypes, and their effects on the biology and physiology of Anticarsia gemmatalis Hübner (Lep.: Noctuidae) were studied. Analysis of covariance and bicoordinate utilization plots were used to remove the effect of feeding time from pupal weight and consumption as well as to separate pre- and postingestive effects of treatment on A. gemmatalis growth. Genotypes PI 274454, PI 227687, and "IAC-100" extracts in general, caused higher mortality, negatively influenced initial larval and pupal weight, and elongated larval cycle. Larvae fed on the "IAC-100" extract diet ingested larger amounts of food per unit of time, but were less efficient in its conversion to biomass. Leaf extracts of PI 227687 had the largest concentration of rutin (quercitin 3-O-rhamnosylglucoside), followed by PI 274454, and "IAC-100"; PI 74454 also had the highest genistin (genistein 7-O-glucoside) content. The susceptible cultivar "BR-16" showed only a kaempferol-based flavonoid in its chemical profile, indicating that after successive crosses, secondary compounds responsible for plant defenses were eliminated. Genotypes PI 274454, PI 227687, and "IAC-100" showed accentuated resistance characteristics and were considered inadequate sources for the development of A. gemmatalis. Considering rutin and genistin concentration in these genotypes, it is suggested that flavonoids are important factors conferring resistance to A. gemmatalis. PMID:16222789

Piubelli, Giorla Carla; Hoffmann-Campo, Clara Beatriz; Moscardi, Flavio; Miyakubo, Sandra Hitomi; de Oliveira, Maria Cristina Neves

2005-07-01

189

Reaction Texture Development in Granulites: A Chemical Potential Approach  

NASA Astrophysics Data System (ADS)

Reaction textures in granulites are generally considered disequilibrium features that are attributed to changes in P-T conditions during a rock's evolution. Various types of reaction textures occur in metamorphic rocks, but can broadly be categorized as either closed or open system. In a closed system, simple reaction textures develop where the products and reactants indicate conservation of the chemical components involved in the reaction. In many rocks, however, more complex reaction textures develop where one or more components must enter into the site where the texture is developing, indicating open system behavior. Once nucleation occurs, and reaction products begin to form, chemical potential gradients are established. Complex reaction textures are difficult to investigate using a standard pseudosection approach. Even for simple reaction textures, conventional pseudosections do not yield information about the spatial organization of a texture. One way to investigate this is to calculate the dependence of phase equilibria on the chemical potentials of the more mobile elements involved in the development of textures. This contribution follows this approach in a case study of sapphirine granulites associated with an exposure of eclogite in the Snowbird tectonic zone of the western Canadian Shield in northern Saskatchewan. Peak P-T conditions in the eclogite reached about 750° and 18 kbar followed by development of extensive reaction textures during near-isothermal decompression through granulite facies conditions. The rock investigated is an impure quartzite containing the peak assemblage Grt + Ky + Qtz with development of silica-undersaturated symplectites of Spl + Spr + An around Ky and coronae of Pl + Opx around Grt. Garnet typically contains abundant inclusions of Ky + Qtz and displays strong Ca-zoning with a decrease in the rim adjacent to surrounding Pl. Opx typically separates Pl from Qtz even in the absence of Grt, occurring as a phase between individual quartz grains and plagioclase. We investigate the phase equilibria and spatial relationships of these textures using petrogenetic grids and compatibility diagrams calculated with THERMOCALC, to understand the effects of chemical potential gradients on the spatial organization and P-T conditions of these reaction textures.

Baldwin, J. A.; Powell, R.

2006-05-01

190

The effect of interfacial resistance on gas absorption with chemical reaction: The film theory model  

Microsoft Academic Search

A simple film theory model yielding a closed?form solution is presented for the analysis of isothermal gas absorption with a chemical reaction taking into account the effect of interfacial resistance. The analysis could be particularly important for a rational design of wet scrubbing systems for gaseous pollutant removal with impurities contaminating the gas?liquid interface. The film theory avoids time dependence

1987-01-01

191

Quantitative global studies of reactomes and metabolomes using a vectorial representation of reactions and chemical compounds  

Microsoft Academic Search

BACKGROUND: Global studies of the protein repertories of organisms are providing important information on the characteristics of the protein space. Many of these studies entail classification of the protein repertory on the basis of structure and\\/or sequence similarities. The situation is different for metabolism. Because there is no good way of measuring similarities between chemical reactions, there is a barrier

Juan C Triviño; Florencio Pazos

2010-01-01

192

Detailed Chemical Kinetic Reaction Mechanism for Oxidation of n-Octane and ISO-Octane.  

National Technical Information Service (NTIS)

The development of detailed chemical kinetic reaction mechanisms for oxidation of n-octane and iso-octane is described, with emphasis on the factors which are specific to many large hydrocarbon fuel molecules. Elements which are of particular importance a...

E. I. Axelsson K. Brezinsky F. L. Dryer W. J. Pitz C. K. Westbrook

1986-01-01

193

Density functional study of chemical reaction equilibrium for dimerization reactions in slit and cylindrical nanopores  

NASA Astrophysics Data System (ADS)

We present a theoretical study of the effects of confinement on chemical reaction equilibrium in slit and cylindrical nanopores. We use a density functional theory (DFT) to investigate the effects of temperature, pore geometry, bulk pressure, transition layering, and capillary condensation on a dimerization reaction that mimics the nitric oxide dimerization reaction, 2NO?(NO)2, in carbonlike slit and cylindrical nanopores in equilibrium with a vapor reservoir. In addition to the DFT calculations, we also utilize the reaction ensemble Monte Carlo method to supplement the DFT results for reaction conversion. This work is an extension of the previous DFT study by Tripathi and Chapman [J. Chem. Phys. 118, 7993 (2003)] on the dimerization reactions confined in the planar slits.

Malijevský, Alexandr; Lísal, Martin

2009-04-01

194

Finite element modeling of contaminant transport in soils including the effect of chemical reactions.  

PubMed

The movement of chemicals through soils to the groundwater is a major cause of degradation of water resources. In many cases, serious human and stock health implications are associated with this form of pollution. Recent studies have shown that the current models and methods are not able to adequately describe the leaching of nutrients through soils, often underestimating the risk of groundwater contamination by surface-applied chemicals, and overestimating the concentration of resident solutes. Furthermore, the effect of chemical reactions on the fate and transport of contaminants is not included in many of the existing numerical models for contaminant transport. In this paper a numerical model is presented for simulation of the flow of water and air and contaminant transport through unsaturated soils with the main focus being on the effects of chemical reactions. The governing equations of miscible contaminant transport including advection, dispersion-diffusion and adsorption effects together with the effect of chemical reactions are presented. The mathematical framework and the numerical implementation of the model are described in detail. The model is validated by application to a number of test cases from the literature and is then applied to the simulation of a physical model test involving transport of contaminants in a block of soil with particular reference to the effects of chemical reactions. Comparison of the results of the numerical model with the experimental results shows that the model is capable of predicting the effects of chemical reactions with very high accuracy. The importance of consideration of the effects of chemical reactions is highlighted. PMID:17270344

Javadi, A A; Al-Najjar, M M

2007-01-09

195

Energy transport effects on rapid bimolecular chemical reactions  

NASA Astrophysics Data System (ADS)

Mass diffusion is known to affect the rate of rapid bimolecular chemical reactions in solution. Rate constants are decreased with respect to their collisional values, an effect which can renormalize the bare rate constant by a factor as large as 100. In this paper we explore the added effect of the thermal diffusivity on rapid reaction rates. This effect arises from the coupling of energy fluctuations to density fluctuations either through the activation energy for reaction or from the heat of reaction. Calculations presented here, using statistical nonequilibrium thermodynamics to calculate the nonequilibrium radial distribution function, show that this effect vanishes in dilute solution. In more concentrated solutions the effect remains negligible unless the diffusion constant is much larger than the thermal diffusivity. Even then the effect is only of the order of 10% of the size of mass diffusion effects in concentrated solutions. Present address: Chemistry Department, University of California, La Jolla, CA 92093, USA.

Keizer, Joel; Peacock-Lopez, Enrique

1987-11-01

196

THE IMPORTANCE OF SPATIAL ACCURACY FOR CHEMICAL INFORMATION MANAGEMENT  

EPA Science Inventory

Information about chemicals can be critical to making timely decisions. The results of these decisions may not be realized for many years. In order to increase the value of chemical information and to create and utilize meaningful environmental models, the Environmental Prote...

197

Importance of Chemical Reactivity in Understanding Environmental Hazard  

Microsoft Academic Search

The focus of the 'Chemistry of Hazardous Materials' course offered during the 1995 fall semester is upon 'chemical reactivity' and its relationship to environmental hazard. The Resource Conservation and Recovery Act (RCRA) defines a hazardous substance as that which exhibits the characteristics of chemical reactivity, corrosivity, ignitability, and toxicity. There are other definitions of hazardous materials that use characteristics that

Charles U. Okonkwo

198

Modelling of gas-solid reaction—Coupling of heat and mass transfer with chemical reaction  

Microsoft Academic Search

A general gas-solid reaction model is formulated. This work is the further development of the previous modelling work of Mazet (1988, Ph.D. Thesis, University of Perpignan) and Goetz (1991, Ph.D. Thesis, University of Perpignan) to simulate reversible gas-solid reactions that have been extensively applied to the new chemical heat pump technology developed at CNRS-IMP. In the present paper, a general

Hui-Bo Lu; Nathalie Mazet; Bernard Spinner

1996-01-01

199

Screening in Low Energy Nuclear Reactions of Importance to Astrophysics  

Microsoft Academic Search

Recent experiments in the LUNAR (Laboratory for Underground Nuclear Astrophysics) project have shown anonymously high electron screening may occur during acceleration driven low energy (<400 kV) ion bombardment of solid targets [1]. These effects become particularly important for E\\/ Ue < 100 (here E= ion energy and Ue = electron-screening potential energy). Thus these effects become significant for the understanding

George H. Miley; Heinz Hora; Nie Luo

2004-01-01

200

Tailoring oxidation degrees of graphene oxide by simple chemical reactions  

SciTech Connect

High quality graphene oxide (GO) with controllable degrees of oxidation was synthesized by simple chemical reactions inspired by approaches to unzip single wall carbon nanotubes using strong oxidizing agents. As compared to the conventional Hummers method, these reactions are less exo-therm involved without emission of toxic gases. The structural characteristics of the synthesized GO with various oxidation degrees were evaluated by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, thermal gravimetric analysis, and UV-vis-IR spectroscopy. GO with tailored degrees of oxidation displays tunable optoelectronic properties and may have a significant impact on developing graphene- or GO-based platforms for various technological applications.

Wang Gongkai [Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning 110004 (China); Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Sun Xiang; Lian Jie [Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Liu Changsheng [Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning 110004 (China)

2011-08-01

201

Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals  

SciTech Connect

We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H{sub 2}CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of H{sub 2}CO. We have decelerated a molecular beam of H{sub 2}CO essentially to rest, producing molecules at 100 mK with a density of {approx}10{sup 6} cm{sup -3}.

Hudson, Eric R.; Ticknor, Christopher; Sawyer, Brian C.; Taatjes, Craig A.; Lewandowski, H. J.; Bochinski, J. R.; Bohn, J. L.; Ye Jun [JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2006-06-15

202

Production of cold formaldehyde molecules for study and control of chemical reaction.  

SciTech Connect

We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H{sub 2}CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of H{sub 2}CO. We have decelerated a molecular beam of H{sub 2}CO essentially to rest, producing molecules at 100 mK with a density of {approx} 10{sup 6} cm{sup -3}.

Taatjes, Craig A.; Bochinski, J. R.; Bohn, John L.; Ye, Jun; Lewandowski, H. J.; Sawyer, Brian C.; Ticknor, Christopher; Hudson, Eric R.

2005-08-01

203

The plasma-chemical reactions of several materials in a rf ion source  

Microsoft Academic Search

The plasma-chemical reactions of several materials are described in this paper. Materials such as quartz and platinum are used for containers of chemical reactions in various fields. Because of their stability chemical reactions do not occur easily, but such reactions can occur within the plasma of a rf ion source, and ion beams of such materials have been extracted from

Bai Gui Bin

1990-01-01

204

Gamma and the Chemical Reaction Model: Fifteen Years After  

Microsoft Academic Search

Gamma was originally proposed in 1986 as a formalism for the definition of programs without artificial sequentiality. The\\u000a basic idea underlying the formalism is to describe computation as a form of chemical reaction on a collection of individual pieces of data. Due to the very minimal nature of the language, and its absence of sequential\\u000a bias, it has been possible

Jean-Pierre Ban?tre; Pascal Fradet; Daniel Le Métayer

205

Separation of the isotopes of boron by chemical exchange reactions  

DOEpatents

The isotopes of boron, .sup.10 B and .sup.11 B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF.sub.3 and a liquid BF.sub.3 . donor molecular addition complex formed between BF.sub.3 gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone.

McCandless, Frank P. (Bozeman, MT); Herbst, Ronald S. (Idaho Falls, ID)

1995-01-01

206

Separation of the isotopes of boron by chemical exchange reactions  

DOEpatents

The isotopes of boron, {sup 10}B and {sup 11}B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF{sub 3} and a liquid BF{sub 3} donor molecular addition complex formed between BF{sub 3} gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone. 1 Fig.

McCandless, F.P.; Herbst, R.S.

1995-05-30

207

Laboratory Kinetics of Chemical Reactions occurring in Astrophysical Environments  

Microsoft Academic Search

To model the dynamics and molecular evolution of interstellar clouds, a great deal of information on chemical kinetics is required, preferably under the appropriate conditions of kinetic temperature and internal excitation. This kinetics includes (i) gas phase ionic (ion-molecule and electron-ion) and (ii) neutral-neutral reactions and (iii) heterogeneous surface catalysis, all from simple species to those as complex as polyaromatic

N. G. Adams; L. M. Babcock

2005-01-01

208

APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems  

SciTech Connect

Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

Nguyen, H.D.

1991-11-01

209

APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems  

SciTech Connect

Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

Nguyen, H.D.

1991-11-01

210

Spatiotemporal regulation of chemical reactions by active cytoskeletal remodeling  

PubMed Central

Efficient and reproducible construction of signaling and sorting complexes, both on the surface and within the living cell, is contingent on local regulation of biochemical reactions by the cellular milieu. We propose that in many cases this spatiotemporal regulation can be mediated by interaction with components of the dynamic cytoskeleton. We show how the interplay between active contractility and remodeling of the cytoskeleton can result in transient focusing of passive molecules to form clusters, leading to a dramatic increase in the reaction efficiency and output levels. The dynamic cytoskeletal elements that drive focusing behave as quasienzymes catalyzing the chemical reaction. These ideas are directly applicable to the cortical actin-dependent clustering of cell surface proteins such as lipid-tethered GPI-anchored proteins, Ras proteins, as well as many proteins that have domains that confer the ability to interact with the actin cytoskeleton. In general such cytoskeletal driven clustering of proteins could be a cellular mechanism to spatiotemporally regulate and amplify local chemical reaction rates in a variety of contexts such as signaling, transcription, sorting, and endocytosis.

Chaudhuri, Abhishek; Bhattacharya, Bhaswati; Gowrishankar, Kripa; Mayor, Satyajit; Rao, Madan

2011-01-01

211

Physio-chemical reactions in recycle aggregate concrete.  

PubMed

Concrete waste constitutes the major proportion of construction waste at about 50% of the total waste generated. An effective way to reduce concrete waste is to reuse it as recycled aggregate (RA) for the production of recycled aggregate concrete (RAC). This paper studies the physio-chemical reactions of cement paste around aggregate for normal aggregate concrete (NAC) and RAC mixed with normal mixing approach (NMA) and two-stage mixing approach (TSMA) by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Four kinds of physio-chemical reactions have been recorded from the concrete samples, including the dehydration of C(3)S(2)H(3), iron-substituted ettringite, dehydroxylation of CH and development of C(6)S(3)H at about 90 degrees C, 135 degrees C, 441 degrees C and 570 degrees C, respectively. From the DSC results, it is confirmed that the concrete samples with RA substitution have generated less amount of strength enhancement chemical products when compared to those without RA substitution. However, the results from the TSMA are found improving the RAC quality. The pre-mix procedure of the TSMA can effectively develop some strength enhancing chemical products including, C(3)S(2)H(3), ettringite, CH and C(6)S(3)H, which shows that RAC made from the TSMA can improve the hydration processes. PMID:18718710

Tam, Vivian W Y; Gao, X F; Tam, C M; Ng, K M

2008-07-15

212

40 CFR 707.20 - Chemical substances import policy.  

Code of Federal Regulations, 2013 CFR

...control of chemicals. At such time as international agreement...entry to any shipment until such time as the certification is properly...voluntarily abandoned within the time periods prescribed in 19 CFR...Region X 1200 Sixth Avenue, Seattle, WA 98101...

2013-07-01

213

Chemical reactions occurring during direct solar reduction of CO2.  

PubMed

At high temperatures carbon dioxide may absorb solar radiation and react to form carbon monoxide and molecular oxygen. The CO, so produced, may be converted by well-established means to a combustible fuel, such as methanol. We intend to make a future demonstration of the solar reduction of CO2 based on these processes. This paper, however, addresses only the problem of preserving, or even enhancing, the initial photolytic CO by quenching the hot gas with colder H2O or CO2. We present model calculations with a reaction mechanism used extensively in other calculations. If a CO2 gas stream is heated and photolyzed by intense solar radiation and then allowed to cool slowly, it will react back to the initial CO2 by a series of elementary chemical reactions. The back reaction to CO2 can be terminated with the rapid addition of CO2, water, or a mixture. Calculations show that a three-fold quench with pure CO2 will stop the reactions and preserve over 90% of the initial photolytic CO. We find that water has one of two effects. It can either increase the CO level, or it can catalyze the recombination of O and CO to CO2. The gas temperature is the determining factor. If the quench gas is not sufficient to keep the temperature below approximately 1100 K, a chain-branching reaction dominates and the reaction to CO2 occurs. If the temperature stays below that level a chain terminating reaction dominates and the CO is increased. The former case occurs below approximately a fourfold quench with a water/CO2 mixture. The later case occurs when the quench is greater than fourfold. We conclude that CO2, H2O, or a mixture may quench the hot gas stream photolyzed by solar radiation and preserve the photolytic CO. PMID:11589409

Lyma, J L; Jensen, R J

2001-09-28

214

Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges  

NASA Astrophysics Data System (ADS)

We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes—ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination—is reviewed. Emphasis is placed on those key reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalyzed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase.

Wakelam, V.; Smith, I. W. M.; Herbst, E.; Troe, J.; Geppert, W.; Linnartz, H.; Öberg, K.; Roueff, E.; Agúndez, M.; Pernot, P.; Cuppen, H. M.; Loison, J. C.; Talbi, D.

2010-10-01

215

The Importance of Chemical Substitutes to Chlorofluorocarbons (CFCs)  

Microsoft Academic Search

The first cholroflurocarbon (CFC), CFC-12 (dichlorodifluoromethane, CCl2F2), was invented by Thomas Midgley, Jr. and Alfred Henne in 1928 by the fluorination reaction of carbon tetrachloride with\\u000a antimony trifluoride, and immediately after it was identified as a best refrigerant in performance, CFC-12 was commercialized\\u000a in 1930 in Du Pont Company as a nonflammable and nontoxic refrigerant to replace toxic refrigerants such

Masaaki Yamabe

216

Compare and contrast the reaction coordinate diagrams for chemical reactions and cytoskeletal force generators.  

PubMed

Reaction coordinate diagrams are used to relate the free energy changes that occur during the progress of chemical processes to the rate and equilibrium constants of the process. Here I briefly review the application of these diagrams to the thermodynamics and kinetics of the generation of force and motion by cytoskeletal motors and polymer ratchets as they mediate intracellular transport, organelle dynamics, cell locomotion, and cell division. To provide a familiar biochemical context for discussing these subcellular force generators, I first review the application of reaction coordinate diagrams to the mechanisms of simple chemical and enzyme-catalyzed reactions. My description of reaction coordinate diagrams of motors and polymer ratchets is simplified relative to the rigorous biophysical treatment found in many of the references that I use and cite, but I hope that the essay provides a valuable qualitative representation of the physical chemical parameters that underlie the generation of force and motility at molecular scales. In any case, I have found that this approach represents a useful interdisciplinary framework for understanding, researching, and teaching the basic molecular mechanisms by which motors contribute to fundamental cell biological processes. PMID:23408787

Scholey, Jonathan M

2013-02-01

217

Compare and contrast the reaction coordinate diagrams for chemical reactions and cytoskeletal force generators  

PubMed Central

Reaction coordinate diagrams are used to relate the free energy changes that occur during the progress of chemical processes to the rate and equilibrium constants of the process. Here I briefly review the application of these diagrams to the thermodynamics and kinetics of the generation of force and motion by cytoskeletal motors and polymer ratchets as they mediate intracellular transport, organelle dynamics, cell locomotion, and cell division. To provide a familiar biochemical context for discussing these subcellular force generators, I first review the application of reaction coordinate diagrams to the mechanisms of simple chemical and enzyme-catalyzed reactions. My description of reaction coordinate diagrams of motors and polymer ratchets is simplified relative to the rigorous biophysical treatment found in many of the references that I use and cite, but I hope that the essay provides a valuable qualitative representation of the physical chemical parameters that underlie the generation of force and motility at molecular scales. In any case, I have found that this approach represents a useful interdisciplinary framework for understanding, researching, and teaching the basic molecular mechanisms by which motors contribute to fundamental cell biological processes.

Scholey, Jonathan M.

2013-01-01

218

Chemical reactions of mercury in combustion flue gases  

Microsoft Academic Search

Atmospheric Hg is present in different physical and chemical forms, which determine its atmospheric transformation and transport\\u000a capacities. The chemistry of Hg in flue gases is thus of importance for the deposition pattern around point source emissions.\\u000a In order to apply Hg cleaning methods in flue gases its speciation is also of importance. To investigate this under realistic\\u000a conditions, a

B. Hall; P. Schager; O. Lindqvist

1991-01-01

219

Chemical reaction and dust formation studies in laboratory hydrocarbon plasmas.  

NASA Astrophysics Data System (ADS)

Plasma chemical reaction studies with relevance to, e.g., Titan's atmosphere have been per-formed in various laboratory plasmas [1,2]. Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH4 /N2 and CH4 /Ar gas mixtures by means of mass spectrometry. The main reaction scheme is production of H2 by fragmenta-tion of CH4 , but also production of larger hydrocarbons like Cn Hm with n up to 10 including formation of different functional CN groups is observed. [1] A. Majumdar and R. Hippler, Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition, Rev. Sci. Instrum. 78, 075103 (2007) [2] H.T. Do, G. Thieme, M. Frühlich, H. Kersten, and R. Hippler, Ion Molecule and Dust Particle Formation in Ar/CH4 , Ar/C2 H2 and Ar/C3 H6 Radio-frequency Plasmas, Contrib. Plasma Phys. 45, No. 5-6, 378-384 (2005)

Hippler, Rainer; Majumdar, Abhijit; Thejaswini, H. C.

220

The influence of overlap interactions on chemical reactions in confinement  

NASA Astrophysics Data System (ADS)

Chemical reactions are often carried out in nano-structured materials due to their large surface area per unit mass. It is, however, difficult to understand fully the role of the nano-structure in many reactions due to the superposition of multiple effects. Such effects include: the reduced dimensionality of the system, the heterogeneity of the pore surfaces, the selective adsorption of reactants/products, catalytic effects, and transport limitations. Experimental studies often show many of these effects at the same time, making the results difficult to interpret. In this work we present results of density functional theory calculations illustrating the influence of overlap interactions (shape-catalytic effects) on chemical reactions. In particular, we show the effect of confinement in small pores on the rates of rotational isomerizations of n-butane, 1-butene and 1,3-butadiene. We find that the rates of these transitions change as the double exponential of the pore size in the molecular sieving limit. These results are a first step towards an integrated model for the design of catalytic materials.

Santiso, Erik E.; Gubbins, Keith E.; George, Aaron M.; Buongiorno Nardelli, Marco

2007-03-01

221

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds.  

National Technical Information Service (NTIS)

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previ...

P. A. Glaude C. Melius W. J. Pitz C. K. Westbrook

2001-01-01

222

Shock-induced and Shock-assisted Solid-state Chemical Reactions in Powder Mixtures.  

National Technical Information Service (NTIS)

Shock compression of powder mixtures can lead to chemical reactions, resulting in the formation of equilibrium as well as nonequilibrium compounds, and rapid increases in temperature. The reactions occur as manifestations of enhanced solid-state chemical ...

N. N. Thadhani

1994-01-01

223

Thermodynamics of Chemical Species Important in Aerospace Technology.  

National Technical Information Service (NTIS)

Presented is a detailed report of recent results and critical analyses of experimental measurements completed or in progress, literature surveys, and new measurement-method developments-for high melting metals and their Aerospace-important compounds. The ...

C. W. Beckett T. B. Douglas

1971-01-01

224

Chemical characteristics of mineral trioxide aggregate and its hydration reaction  

PubMed Central

Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed.

2012-01-01

225

Quantum control of chemical reaction dynamics in a classical way  

NASA Astrophysics Data System (ADS)

A simplified approach to quantum control of chemical reaction dynamics based on a classical, local control theory was developed. The amplitude of the control pulse is proportional to the linear momentum of the reaction system within the dipole approximation for the system-radiation field interaction. The kinetic energy of the system is the controlling parameter. That is, the reaction is controlled by accelerating the representative point on a potential energy surface before crossing over a potential barrier and then by deaccelerating it to the target after passing over the potential barrier. The classical treatment was extended to control of wave packet dynamics by replacing the classical momentum by a quantum mechanically averaged momentum on the basis of the Ehrenfest theorem. The present method was applied to a quantum system of a simple one-dimensional, double-well potential for checking its validity. A restriction of the applicability of the simplified method was also discussed. An isomerization of HCN was treated as a model system for wave packet control of a two-dimensional reaction.

Umeda, Hiroaki; Fujimura, Yuichi

2000-09-01

226

On the chemical reaction of matter with antimatter.  

PubMed

A chemical reaction between the building block antiatomic nucleus, the antiproton (p or H- in chemical notation), and the hydrogen molecular ion (H2+) has been observed by the ATHENA collaboration at CERN. The charged pair interact via the long-range Coulomb force in the environment of a Penning trap which is purpose-built to observe antiproton interactions. The net result of the very low energy collision of the pair is the creation of an antiproton-proton bound state, known as protonium (Pn), together with the liberation of a hydrogen atom. The Pn is formed in a highly excited, metastable, state with a lifetime against annihilation of around 1 micros. Effects are observed related to the temperature of the H2+ prior to the interaction, and this is discussed herein. PMID:17492700

Lodi Rizzini, Evandro; Venturelli, Luca; Zurlo, Nicola

2007-06-01

227

Monte-Carlo simulations of chemical reactions in molecular crystals  

NASA Astrophysics Data System (ADS)

Chemical reactions in molecular crystals, yielding new entities (dimers, trimers,..., polymers) in the original structure, are simulated for the first time by stochastic Monte Carlo methods. The results are compared with those obtained by deterministic methods. They show that numerical simulation is a tool for understanding the evolution of these mixed systems. They are in kinetic and not in thermodynamic control. Reactive site distributions, x-ray diffuse scattering, and chain length distributions can be simulated. Comparisons are made with deterministic models and experimental results obtained in the case of the solid state dimerization of cinnamic acid in the beta phase and in the case of the solid state polymerization of diacetylenes.

Even, J.; Bertault, M.

1999-01-01

228

Structural cluster analysis of chemical reactions in solution  

NASA Astrophysics Data System (ADS)

We introduce a simple and general approach to the problem of clustering structures from atomic trajectories of chemical reactions in solution. By considering distance metrics which are invariant under permutation of identical atoms or molecules, we demonstrate that it is possible to automatically resolve as distinct structural clusters the configurations corresponding to reactants, products, and transition states, even in presence of atom-exchanges and of hundreds of solvent molecules. Our approach strongly simplifies the analysis of large trajectories and it opens the way to the construction of kinetic network models of activated processes in solution employing the available efficient schemes developed for proteins conformational ensembles.

Gallet, Grégoire A.; Pietrucci, Fabio

2013-08-01

229

A topological stochastic approach to the study of multidimensional potential energy surfaces of chemical reactions  

Microsoft Academic Search

In this article we propose a new approach for investigating the properties of multidimensional potential energy surfaces in chemical reactions, based on relations of each multidimensional surface to its one-dimensional image which is the chemical reaction tree. This approach makes it possible to find a common number of independent channels in chemical reactions for complex systems and to construct the

Igor V. Krivoshey; Liudmila A. Sleta

1976-01-01

230

Modeling the influence of chemical reactions on the mechanisms of ionic transport in porous materials  

Microsoft Academic Search

This paper attempts to critically review various approaches developed to model the effects of chemical reactions on the mechanisms of ionic transport in porous media. A comprehensive overview of the various types of chemical reactions that can occur in reactive porous solids is first presented. Methods to model each of these chemical reactions are then described and analyzed. The ability

E. Samson; J. Marchand; J. J. Beaudoin

2000-01-01

231

A Model for Incorporating Chemical Reactions in Mesoscale Modeling of Laser Ablation of Polymers  

Microsoft Academic Search

We have developed a methodology for including effects of chemical reactions in coarse-grained computer simulations such as those that use the united atom or bead and spring approximations. The new coarse-grained chemical reaction model (CGCRM) adopts the philosophy of kinetic Monte Carlo approaches and includes a probabilistic element to predicting when reactions occur, thus obviating the need for a chemically

Barbara J. Garrison; Yaroslava G. Yingling

2004-01-01

232

Theory of reversible associative-dissociative diffusion-influenced chemical reaction. II. Bulk reaction  

NASA Astrophysics Data System (ADS)

A many-particle homogeneous reacting system of reactants, where bulk reversible reaction A + B <--> C takes place, is considered in the framework of the kinetic theory approach. The various forms of kinetic equations in the thermodynamic limit are obtained, and important relations between kinetic coefficients characterizing the course of bulk and the corresponding geminate reactions are established. Based on the kinetic equations derived, different results available in the literature have been analyzed. Universal long-term kinetic laws of the reaction course are deduced.

Kipriyanov, Alexey A.; Doktorov, Alexander B.

2013-01-01

233

The study of thermodynamic properties and transport properties of multicomponent systems with chemical reactions  

NASA Astrophysics Data System (ADS)

In case of system with chemical reaction the most important properties are heat conductivity and heat capacity. In this work we have considered the equation for estimate the component of these properties caused by chemical reaction and ionization processes. We have evaluated the contribution of this part in heat conductivity and heat capacity too. At the high temperatures contribution in heat conductivity from ionization begins to play an important role. We have created a model, which describe partial and full ionization of gases and gas mixtures. In addition, in this work we present the comparison of our result with experimental data and data from numerical simulation. We was used the data about transport properties of middle composition of Russian coals and the data of thermophysical properties of natural gas for comparison.

Shmelkov, Y.; Samujlov, E.

2013-04-01

234

Analysis of initial reactions of MALDI based on chemical properties of matrixes and excitation condition.  

PubMed

This investigation concerns the initial chemical reactions that affect the ionization of matrixes in matrix-assisted laser desorption/ionization (MALDI). The study focuses on the relaxations of photon energy that occur on a comparable time scale to that of ionization, in which the available laser energy is shared and the ionization condition is changed. The relaxations include fluorescence, fragmentation, and nonradiative relaxation from the excited state to the ground state. With high absorption cross section and long excited-state lifetime, photoionization of matrix plays an important role if sufficient laser energy is used. Under other conditions, thermal ionization of the molecule in the ground state is predicted to be one of the important reactions. Evidence of change in the branching ratio of initial reactions with the matrix and the excitation wavelength was obtained with ?-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, and 2,4,6-trihydroxyacetophenone. These matrixes are studied by obtaining their mixed crystal absorption spectra, fluorescence properties, laser-induced infrared emission, and product ions. The exact ionization pathway depends on the chemical properties of matrixes and the excitation conditions. This concept may explain the diversity of experimental results observed in MALDI experiments, which provides an insight into the ensemble of chemical reactions that govern the generation of ions. PMID:22799495

Lai, Yin-Hung; Wang, Chia-Chen; Chen, Chiu Wen; Liu, Bo-Hong; Lin, Sheng Hsien; Lee, Yuan Tseh; Wang, Yi-Sheng

2012-08-01

235

Effects of exothermic chemical reaction on the photoacoustic effect from particulate suspensions  

Microsoft Academic Search

Irradiation of chemically reactive particulate suspensions by high power, pulsed laser radiation initiates reactions at the sites of the particles so that besides the absorbed optical energy, chemical energy is liberated. In addition to the release of chemical energy, chemical reaction can result in gas production both of which result in enhancement in the amplitude of the photoacoustic effect. Here

Han Jung Park; Binbin Wu; Gerald J. Diebold

2011-01-01

236

Mass Spectroscopy of Chemical Reaction of 3d Metal Clusters Involved in Chemical Vapor Deposition Synthesis of Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

The chemical reactions of transition metal clusters in the gas phase have aroused considerable scientific interest and are also of critical scientific importance. For example, these reactions are involved in the synthesis of single-walled carbon nanotubes, which are considered ideal materials because of their outstanding properties. Alcohol catalytic chemical vapor deposition (ACCVD) is one of the best synthetic processes for carbon nanotubes (CNTs); however, even the initial growth mechanism is still unclear, unlike those of other synthetic processes. In this study, we used a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to determine the initial reactions of transition metal cluster ions (iron, cobalt, and nickel) that are typically adopted in the alcohol CVD process. Metal clusters with approximately 10-25 atoms each, generated by a pulsed laser ablation system in a supersonic-expansion cluster beam source, were directly carried into the FT-ICR cell. Subsequently, ethanol was introduced into the ICR cell. We observed two different results: one was simple chemisorption observed in the iron cluster and the other was dehydrogenated chemisorption observed in the nickel cluster; however, cobalt clusters exhibited both patterns, and a sequential reaction was observed. Furthermore, the dehydrogenation of ethanol on the cobalt cluster is fully described from isotope-labeled experiments.

Inoue, Shuhei; Maruyama, Shigeo

2008-04-01

237

Chemical functionalization of diamond surfaces by reaction with diaryl carbenes.  

PubMed

A rapid route to the chemical functionalization of hydrogen-terminated diamond surfaces deposited by chemical vapor deposition involving their reaction with substituted diaryl carbenes has been investigated. To avoid difficulties in the handling of highly reactive compounds, the carbene is generated in situ from the thermal decomposition at 400 K of a thin film of the corresponding diaryl diazomethane precursor deposited at the diamond interface. X-ray photoelectron spectroscopy (XPS) has been used to verify that surface functionalization using two starting compounds, bis(4-iodophenyl) diazomethane and bis(4-nitrophenyl) diazomethane, can be achieved using this approach in agreement with recent theoretical studies. The surface grafting density is measured to be around 10(14) cm(-2) in each case. The chemistry observed is found to be insensitive to the detailed properties of the diamond film and to the presence of oxygen contamination at the hydrogen-terminated diamond surface. We further demonstrate the utility of the approach, in the case of the bound nitrophenyl compound, by its reduction to the corresponding primary amine followed by reaction with fluorescein isothiocyanate to achieve fluorescent tagging of the diamond interface. PMID:18177059

Wang, Hao; Griffiths, Jon-Paul; Egdell, Russell G; Moloney, Mark G; Foord, John S

2008-01-05

238

An Overview of Chemical Processes That Damage Cellular DNA: Spontaneous Hydrolysis, Alkylation, and Reactions with Radicals  

PubMed Central

The sequence of heterocyclic bases on the interior of the DNA double helix constitutes the genetic code that drives the operation of all living organisms. With this said, it is not surprising that chemical modification of cellular DNA can have profound biological consequences. Therefore, the organic chemistry of DNA damage is fundamentally important to diverse fields including medicinal chemistry, toxicology, and biotechnology. This review is designed to provide a brief overview of the common types of chemical reactions that lead to DNA damage under physiological conditions.

Gates, Kent S.

2009-01-01

239

Machine learning of chemical reactivity from databases of organic reactions.  

PubMed

Databases of chemical reactions contain knowledge about the reactivity of specific reagents. Although information is in general only explicitly available for compounds reported to react, it is possible to derive information about substructures that do not react in the reported reactions. Both types of information (positive and negative) can be used to train machine learning techniques to predict if a compound reacts or not with a specific reagent. The whole process was implemented with two databases of reactions, one involving BuNH2 as the reagent, and the other NaCNBH3. Negative information was derived using MOLMAP molecular descriptors, and classification models were developed with Random Forests also based on MOLMAP descriptors. MOLMAP descriptors were based exclusively on calculated physicochemical features of molecules. Correct predictions were achieved for approximately 90% of independent test sets. While NaCNBH3 is a selective reducing reagent widely used in organic synthesis, BuNH2 is a nucleophile that mimics the reactivity of the lysine side chain (involved in an initiating step of the mechanism leading to skin sensitization). PMID:19468693

Carrera, Gonçalo V S M; Gupta, Sunil; Aires-de-Sousa, João

2009-05-26

240

Nanoscale wear as a stress-assisted chemical reaction  

NASA Astrophysics Data System (ADS)

Wear of sliding contacts leads to energy dissipation and device failure, resulting in massive economic and environmental costs. Typically, wear phenomena are described empirically, because physical and chemical interactions at sliding interfaces are not fully understood at any length scale. Fundamental insights from individual nanoscale contacts are crucial for understanding wear at larger length scales, and to enable reliable nanoscale devices, manufacturing and microscopy. Observable nanoscale wear mechanisms include fracture and plastic deformation, but recent experiments and models propose another mechanism: wear via atom-by-atom removal (`atomic attrition'), which can be modelled using stress-assisted chemical reaction kinetics. Experimental evidence for this has so far been inferential. Here, we quantitatively measure the wear of silicon--a material relevant to small-scale devices--using in situ transmission electron microscopy. We resolve worn volumes as small as 25 +/- 5 nm3, a factor of 103 lower than is achievable using alternative techniques. Wear of silicon against diamond is consistent with atomic attrition, and inconsistent with fracture or plastic deformation, as shown using direct imaging. The rate of atom removal depends exponentially on stress in the contact, as predicted by chemical rate kinetics. Measured activation parameters are consistent with an atom-by-atom process. These results, by direct observation, establish atomic attrition as the primary wear mechanism of silicon in vacuum at low loads.

Jacobs, Tevis D. B.; Carpick, Robert W.

2013-02-01

241

Chemical kinetics of the gas-phase reaction between uranium hexafluoride and hydrogen  

SciTech Connect

A study was made of the chemical kinetics of the homogeneous gas-phase reaction between uranium hexafluoride and hydrogen by measuring the rate of disappearance of UF/sub 6/. It has been concluded that the rate-limiting step for which the kinetics have been measured is UF/sub 6/ + HF + H (2). The reaction has been studied in a steady-state flow system over a temperature range of approx.625 to 825 K. Various surface-to-volume ratios were employed to aid in distinguishing gas-phase reactions from surface reactions. The steady-state concentration of the UF/sub 6/ after reaction with H/sub 2/ was monitored in a special multipass infrared spectrophotometer at the 626-cm/sup -1/ absorption band of UF/sub 6/. The principal problems were corrosion, plugging, surface intrusion, and the deleterious effects of minute traces of water; these problems have greatly slowed progress in this field. Several series of measurements involving different initial species concentrations and residence times, with each series at constant temperature, show that the rate is first order in UF/sub 6/. Our measurements yield a dependable Arrhenius curve in terms of a second-order expression for k, the bimolecular specific reaction rate constant for the disappearance of UF/sub 6/. It is believed that this overall rate of the disappearance of UF/sub 6/ is somewhat less than twice that of the critical reaction step 2, indicated above, so that the specific reaction rate constant k/sub 2/ is approx.8.7 c 10/sup 14/ exp(-34550 kcal/RT) cm/sup 3/ mol/sup -1/ s/sup -1/. Conclusions have been reached concerning the relative importance of the various elementary reaction steps involved in the chemical mechanism.

Myerson, A.L. (Mote Marine Lab., Sarasota, FL); Chludzinski, J.J. Jr.

1981-12-10

242

Some Nuclear Reaction Rates of Importance for Nucleosynthesis around Mass 45  

Microsoft Academic Search

This thesis describes the measurement of absolute cross sections and the determination of thermonuclear reaction rates for a series of reactions which are of importance in stellar nucleosynthesis. The yield of (gamma)-rays from the reaction ('42)Ca(p,(gamma))('43)Sc has been measured as a function of bombarding energy over the range 0.63 - 3.01 MeV, from ('44)Ca(p,(gamma))('45)Sc over the range 0.775 - 4.00

Leon William Mitchell

1985-01-01

243

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.  

SciTech Connect

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2010-06-01

244

Convective--Diffusive Transport with Chemical Reaction in Natural Convection Flows  

Microsoft Academic Search

:  A study of laminar natural convection flow over a semi-infinite vertical plate at constant species concentration is examined.\\u000a The plate is maintained at a given concentration of some chemical species while convection is induced by diffusion into and\\u000a chemical reaction with the ambient fluid. In the absence of chemical reaction, a similarity transform is possible. When chemical\\u000a reaction occurs, perturbation

M. Rahman; I. Mulolani

2000-01-01

245

Product Studies of the Atmospherically-Important Reactions of Alkenes and Aromatic Hydrocarbons.  

National Technical Information Service (NTIS)

Alkenes and aromatic hydrocarbons are important constituents of ambient air in polluted urban areas, and their atmospheric reactions in the presence of oxides of nitrogen lead to the formation of ozone and other manifestations of photochemical air polluti...

R. Atkinson J. Arey E. C. Tuazon

1997-01-01

246

Coupling of hydrologic transport and chemical reactions in a stream affected by acid mine drainage  

USGS Publications Warehouse

Experiments in St. Kevin Gulch, an acid mine drainage stream, examined the coupling of hydrologic transport to chemical reactions affecting metal concentrations. Injection of LiCl as a conservative tracer was used to determine discharge and residence time along a 1497-m reach. Transport of metals downstream from inflows of acidic, metal-rich water was evaluated based on synoptic samples of metal concentrations and the hydrologic characteristics of the stream. Transport of SO4 and Mn was generally conservative, but in the subreaches most affected by acidic inflows, transport was reactive. Both 0.1-??m filtered and particulate Fe were reactive over most of the stream reach. Filtered Al partitioned to the particulate phase in response to high instream concentrations. Simulations that accounted for the removal of SO4, Mn, Fe, and Al with first-order reactions reproduced the steady-state profiles. The calculated rate constants for net removal used in the simulations embody several processes that occur on a stream-reach scale. The comparison between rates of hydrologie transport and chemical reactions indicates that reactions are only important over short distances in the stream near the acidic inflows, where reactions occur on a comparable time scale with hydrologic transport and thus affect metal concentrations.

Kimball, B. A.; Broshears, R. E.; Bencala, K. E.; McKnight, D. M.

1994-01-01

247

Chemical reactions of excited nitrogen atoms for short wavelength chemical lasers. Final technical report  

SciTech Connect

Accomplishments of this program include the following: (1) Scalable, chemical generation of oxygen atoms by reaction of fluorine atoms and water vapor. (2) Production of nitrogen atom densities of 1 {times} 10{sup 1}5 cm{sup {minus}3} with 5% electrical efficiency by injecting trace amounts of fluorine into microwave discharged nitrogen. (3) Production of cyanide radicals by reaction of high densities of N atoms with cyanogen. (4) Production of carbon atoms by reaction of nitrogen atoms with cyanogen or with fluorine atoms and hydrogen cyanide. (5) Confirmation that the reaction of carbon atoms and carbonyl sulfide produces CS(a{sup 3} {Pi}{sub r}), as predicted by conservation of electron spin and orbital angular momenta and as proposed by others under another SWCL program. (6) Production of cyanide radicals by injection of cyanogen halides into active nitrogen and use as spectroscopic calibration source. (7) Demonstration that sodium atoms react with cyanogen chloride, bromide and iodide and with cyanuric trifluoride to produce cyanide radicals. (8) Demonstration of the potential utility of the fluorine atom plus ammonia reaction system in the production of NF(b{sup l}{Sigma}{sup +}) via N({sup 2}D) + F{sub 2}.

Not Available

1989-12-15

248

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

This is the final technical report for the project titled 'Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks'. The aim of the project was to develop an efficient chemistry model for combustion simulations. The reduced chemistry model was developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) was used via a new network topology known as Non-linear Principal Components Analysis (NPCA). A commonly used Multilayer Perceptron Neural Network (MLP-NN) was modified to implement NPCA-NN. The training rate of NPCA-NN was improved with the GEneralized Regression Neural Network (GRNN) based on kernel smoothing techniques. Kernel smoothing provides a simple way of finding structure in data set without the imposition of a parametric model. The trajectory data of the reaction mechanism was generated based on the optimization techniques of genetic algorithm (GA). The NPCA-NN algorithm was then used for the reduction of Dimethyl Ether (DME) mechanism. DME is a recently discovered fuel made from natural gas, (and other feedstock such as coal, biomass, and urban wastes) which can be used in compression ignition engines as a substitute for diesel. An in-house two-dimensional Computational Fluid Dynamics (CFD) code was developed based on Meshfree technique and time marching solution algorithm. The project also provided valuable research experience to two graduate students.

Ziaul Huque

2007-08-31

249

Mechanisms of prion disease progression: a chemical reaction network approach.  

PubMed

Fatal neurodegenerative diseases such as bovine spongiform encephalopathy in cattle, scrapie in sheep and Creutzfeldt-Jakob disease in humans are caused by prions. Prion is a protein encoded by a normal cellular gene. The cellular form of the prion, namely PrP(C), is benign but can be converted into a disease-causing form (named scrapie), PrP(Sc), by a conformational change from -helix to -sheets. Prions replicate by this conformational change; that is, PrP(Sc) interacts with PrP(C) producing a new molecule of PrP(Sc). This kind of replication is modelled in this contribution as an autocatalytic process. The kinetic model accounts for two of the three epidemiological manifestations: sporadic and infectious. By assuming irreversibility of the PrP(Sc) replication and describing a first-order reaction for the degradation of cellular tissue, the authors explore dynamical scenarios for prion progression, such as oscillations and conditions for multiplicity of equilibria. Feinberg's chemical reaction network theory is exploited to identify multiple steady states and their associate kinetic constants. PMID:22129030

Méndez, J M; Femat, R

2011-11-01

250

Site remediation via Dispersion by Chemical Reaction (DCR). Special report  

SciTech Connect

The DCR (Dispersion by Chemical Reaction) technologies are a group of patented waste treatment processes using CaO (quicklime) for the immobilization of heavily oiled sludges, oil-contaminated soils, acid-tars, and heavy metals in Ca(OH)2 and CaCO3 matrices. The objectives of this project were to: (1) evaluate the DCR process for remediating soils contaminated with pesticides, petroleum hydrocarbons (oils and fuels), and heavy metals in cold regions and (2) evaluate DCR-treated oil-contaminated soil as a non-frost-susceptible (NFS) construction material. Three major studies evaluated the DCR process to remediate (1) hydrocarbons at Eareckson Air Force Station on Shemya in the Aleutians, (2) pesticide-contaminated soils from Rocky Mt. Arsenal, and (3) heavy-metal contaminated soils from a former zinc smelter site at Palmerton, Pennsylvania. The DCR process was successful in stabilizing liquid organics and heavy metals in contaminated soils. The chemical properties of soils contaminated by solid organics (asphalt tar and pesticides) were not generally improved by the DCR process, but even in these cases, the physical properties were improved for potential reuse as construction materials.

Marion, G.M.; Payne, J.R.; Brar, G.S.

1997-08-01

251

High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions  

Microsoft Academic Search

In this article, we describe an apparatus in our laboratory for investigating elementary chemical reactions using the high resolution time-of-flight Rydberg tagging method. In this apparatus, we have adopted a rotating source design so that collision energy can be changed for crossed beam studies of chemical reactions. Preliminary results on the HI photodissociation and the F atom reaction with H2

Minghui Qiu; Li Che; Zefeng Ren; Dongxu Dai; Xiuyan Wang; Xueming Yang

2005-01-01

252

Diffusion of Weak Acids across Lipid Bilayer Membranes: Effects of Chemical Reactions in the Unstirred Layers  

Microsoft Academic Search

Chemical reactions in the aqueous unstirred layers of solution adjacent to a membrane can have dramatic effects on the diffusion of solutes across that membrane. This is demonstrated by the diffusion of labeled salicylate and salicylic acid across a phospholipid bilayer membrane. Two types of chemical reactions are considered. The first is an isotopic exchange reaction between the ionic and

John Gutknecht; D. C. Tosteson

1973-01-01

253

Progression in High School Students' (Aged 16-18) Conceptualizations about Chemical Reactions in Solution.  

ERIC Educational Resources Information Center

|Explores the development over time of students' understandings of the concept of chemical reaction in the context of two familiar reactions in solution. Based on interviews (n=48), results show that students made some progress in their understanding of the concept of chemical reaction but some fundamental misconceptions remained. (Author/MM)|

Boo, Hong-Kwen; Watson, J. R.

2001-01-01

254

Progression in High School Students' (Aged 16-18) Conceptualizations about Chemical Reactions in Solution.  

ERIC Educational Resources Information Center

Explores the development over time of students' understandings of the concept of chemical reaction in the context of two familiar reactions in solution. Based on interviews (n=48), results show that students made some progress in their understanding of the concept of chemical reaction but some fundamental misconceptions remained. (Author/MM)

Boo, Hong-Kwen; Watson, J. R.

2001-01-01

255

On the role of van der Waals interaction in chemical reactions at low temperatures  

Microsoft Academic Search

It is shown that van der Waals interaction potential plays a crucial role in chemical reactions at low temperatures. By taking the Cl+HD reaction as an illustrative example, we demonstrate that quasibound states of the van der Waals potential preferentially undergo chemical reaction rather than vibrational predissociation. Prereaction occurs even when the wave functions of the quasibound states peak far

N. Balakrishnan

2004-01-01

256

Shock-induced and shock-assisted solid-state chemical reactions in powder mixtures  

Microsoft Academic Search

Shock compression of powder mixtures can lead to chemical reactions, resulting in the formation of equilibrium as well as nonequilibrium compounds, and rapid increases in temperature. The reactions occur as manifestations of enhanced solid-state chemical reactivity of powders, caused by configurational changes and defect states introduced during shock compression. Two types of reactions are possible and can be distinguished on

N. N. Thadhani

1994-01-01

257

Simplifying the Jacobian Criterion for precluding multistationarity in chemical reaction networks  

Microsoft Academic Search

Chemical reaction networks taken with mass-action kinetics are dynamical systems that arise in chemical engineering and systems biology. In general, determining whether a chemical reaction network admits multiple steady states is difficult, as this requires determining existence of multiple positive solutions to a large system of polynomials with unknown coefficients. However, in certain cases, various easy criteria can be applied.

Badal Joshi; Anne Shiu

2011-01-01

258

Control of gaseous pollutants from industrial combustion by chemical reaction. Paper 81. 35. 7  

Microsoft Academic Search

The control methods for gaseous emissions from industrial combustion sources by chemical reaction processes is reviewed. The applicability and effectiveness of chemical control techniques, equipment operation and process limitations are discussed. In some cases, the control of gases by chemical reaction may be appropriate for achieving stringest control requirements. 30 refs.

J. D. Mobley; K. J. Lim

1981-01-01

259

Binuclear metallohydrolases: complex mechanistic strategies for a simple chemical reaction.  

PubMed

Binuclear metallohydrolases are a large family of enzymes that require two closely spaced transition metal ions to carry out a plethora of hydrolytic reactions. Representatives include purple acid phosphatases (PAPs), enzymes that play a role in bone metabolism and are the only member of this family with a heterovalent binuclear center in the active form (Fe(3+)-M(2+), M = Fe, Zn, Mn). Other members of this family are urease, which contains a di-Ni(2+) center and catalyzes the breakdown of urea, arginase, which contains a di-Mn(2+) center and catalyzes the final step in the urea cycle, and the metallo-?-lactamases, which contain a di-Zn(2+) center and are virulence factors contributing to the spread of antibiotic-resistant pathogens. Binuclear metallohydrolases catalyze numerous vital reactions and are potential targets of drugs against a wide variety of human disorders including osteoporosis, various cancers, antibiotic resistance, and erectile dysfunctions. These enzymes also tend to catalyze more than one reaction. An example is an organophosphate (OP)-degrading enzyme from Enterobacter aerogenes (GpdQ). Although GpdQ is part of a pathway that is used by bacteria to degrade glycerolphosphoesters, it hydrolyzes a variety of other phosphodiesters and displays low levels of activity against phosphomono- and triesters. Such a promiscuous nature may have assisted the apparent recent evolution of some binuclear metallohydrolases to deal with situations created by human intervention such as OP pesticides in the environment. OP pesticides were first used approximately 70 years ago, and therefore the enzymes that bacteria use to degrade them must have evolved very quickly on the evolutionary time scale. The promiscuous nature of enzymes such as GpdQ makes them ideal candidates for the application of directed evolution to produce new enzymes that can be used in bioremediation and against chemical warfare. In this Account, we review the mechanisms employed by binuclear metallohydrolases and use PAP, the OP-degrading enzyme from Agrobacterium radiobacter (OPDA), and GpdQ as representative systems because they illustrate both the diversity and similarity of the reactions catalyzed by this family of enzymes. The majority of binuclear metallohydrolases utilize metal ion-activated water molecules as nucleophiles to initiate hydrolysis, while some, such as alkaline phosphatase, employ an intrinsic polar amino acid. Here we only focus on catalytic strategies applied by the former group. PMID:22698580

Schenk, Gerhard; Miti?, Nataša; Gahan, Lawrence R; Ollis, David L; McGeary, Ross P; Guddat, Luke W

2012-06-14

260

Chemical dynamics in the gas phase : quantum mechanics of chemical reactions.  

SciTech Connect

This research program focuses on both the development and application of accurate quantum mechanical methods to describe gas phase chemical reactions and highly excited molecules. Emphasis is often placed on time-dependent or integrative approaches that, in addition to computational simplifications, yield useful mechanistic insights. Applications to systems of current experimental and theoretical interest are emphasized. The results of these calculations also allow one to gauge the quality of the underlying potential energy surfaces and the reliability of more approximate theoretical approaches such as classical trajectories and transition state theories.

Gray, S. K.

1999-07-02

261

Chemical nature and reaction mechanisms of the molybdenum cofactor of xanthine oxidoreductase.  

PubMed

Xanthine oxidoreductase (XOR), a complex flavoprotein, catalyzes the metabolic reactions leading from hypoxanthine to xanthine and from xanthine to urate, and both reactions take place at the molybdenum cofactor. The enzyme is a target of drugs for therapy of gout or hyperuricemia. We review the chemical nature and reaction mechanisms of the molybdenum cofactor of XOR, focusing on molybdenum-dependent reactions of actual or potential medical importance, including nitric oxide (NO) synthesis. It is now generally accepted that XOR transfers the water-exchangeable -OH ligand of the molybdenum atom to the substrate. The hydroxyl group at OH-Mo(IV) can be replaced by urate, oxipurinol and FYX-051 derivatives and the structures of these complexes have been determined by xray crystallography under anaerobic conditions. Although formation of NO from nitrite or formation of xanthine from urate by XOR ischemically feasible, it is not yet clear whether these reactions have any physiological significance since the reactions are catalyzed at a slow rate even under anaerobic conditions. PMID:23116398

Okamoto, Ken; Kusano, Teruo; Nishino, Takeshi

2013-01-01

262

Importance of equilibrium fluctuations between most stable conformers in the control of the reaction mechanism.  

PubMed

Hydrolysis of closely related compounds show how subtle structural differences markedly change reaction mechanisms. While in the hydrolysis of 3-acetoxy-2-naphthoic acid (3AC2NA) the reacting groups rotate freely, favoring intramolecular general base catalysis, the 1-acetoxy-2-naphthoic acid (1AC2NA) isomer is caged in an energy wall that freezes a conformation suitable for intramolecular nucleophilic attack, in contrast to the results expected for reactions governed largely by electronic effects. The results highlight the importance of the dynamics of equilibrium fluctuations between most stable conformers in the control of the reaction mechanism, (i) promoting the nucleophilic attack in 1AC2NA by allowing the most stable conformers to equilibrate only via rotation in a direction that intercepts the reaction coordinate and (ii) favoring a general base-catalyzed water attack in 3AC2NA by favoring equilibration via rotation that allows inclusion of a water molecule in a proper position for reaction. PMID:20931978

Souza, Bruno S; Nome, Faruk

2010-11-01

263

Measurements and analysis of alpha-induced reactions of importance for nuclear astrophysics  

NASA Astrophysics Data System (ADS)

Reactions during stellar helium burning are of primary importance for understanding nucleosynthesis. A detailed understanding of the critical reaction chain 4He(2alpha, gamma)12C( alpha, gamma)16O(alpha, gamma) 20Ne is necessary both because it is the primary energy source and because it determines the ratio of 12C to 16O produced, which in turn significantly effects subsequent nucleosynthesis. Also during Helium burning, the reactions 22Ne(alpha, n)25Mg and 22Ne(alpha, gamma )26Mg are crucial in determining the amount of neutrons available for the astrophysical s-process. This thesis presents new experimental results concerning the 16O(alpha, gamma) 20Ne, 22Ne(alpha, n)25Mg, and 22Ne(alpha, gamma)26Mg reaction rates. These results are then applied to the calculation of the associated stellar reaction rates in order to achieve better accuracy.

de Messieres, Genevieve Escande

2011-11-01

264

Model-free Investigation of Ultrafast Bimolecular Chemical Reactions: Bimolecular Photo Induced Electron Transfer  

NASA Astrophysics Data System (ADS)

Using photoinduced bimolecular electron transfer reactions as example we demonstrate how diffusion controlled bimolecular chemical reactions can be studied in a model-free manner by quantitatively combining different ultrafast spectroscopical tools.

Lang, Bernhard; Rosspeintner, Arnulf; Vauthey, Eric

2013-03-01

265

Product studies of the atmospherically-important reactions of alkenes and aromatic hydrocarbons. Final report  

Microsoft Academic Search

Alkenes and aromatic hydrocarbons are important constituents of ambient air in polluted urban areas, and their atmospheric reactions in the presence of oxides of nitrogen lead to the formation of ozone and other manifestations of photochemical air pollution. During this Contract, the products and mechanisms of the gas-phase OH radical-initiated and O3 reactions of a series of alkenes and of

R. Atkinson; J. Arey; E. C. Tuazon

1997-01-01

266

Beyond transition state theory: Rigorous quantum approaches for determining chemical reaction rates  

SciTech Connect

Transition state theory (TST) has historically been the most important and widely used theoretical approach for describing the rates of chemical reactions, and for qualitative pictures and order-of-magnitude estimates one does not expect this situation to change. However a rigorous, quantitative treatment of chemical reaction rates must go beyond TST. A rigorous description, for example, must be based on a quantum mechanical description of the molecular system, but the fundamental assumption on which TST is based - namely that the molecular dynamics is {open_quotes}direct,{close_quotes} i.e., that no trajectories re-cross a dividing surface which separates reactants and products (vide infra) - is couched inherently in the language of classical mechanics. There is no unambiguous way to quantize TST, for the various ways of trying to do so invariably require one to introduce additional assumptions about the reaction dynamics. As one tries to eliminate these {open_quotes}additional assumptions{close_quotes} one is driven ultimately to an exact quantum treatment of the reaction dynamics which is then no longer a transition state theory (i.e., approximation) but simply an exact formulation. It is such exact approaches, those without inherent approximations, that are the subject of this chapter.

Miller, W.H.

1995-01-01

267

Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory  

NASA Astrophysics Data System (ADS)

The purpose of this article is to discuss two colorful reactions not widely used by chemical educators in high schools or college chemistry laboratories: The synthesis of zinc iodide from its elements, zinc and iodine, and the subsequent decomposition of zinc iodide back into its elements. These reactions are important for chemistry teachers to know about because they can be performed by introductory students to understand different aspects of chemical change such as the concepts of reaction, compound, bonding, excess and limiting reactants, an empirical formula, balanced chemical equation, the conservation of matter and energy, the Law of the Conservation of Mass, and the Law of Constant Composition. These concepts, in turn, are important because they are fundamental to chemistry, are widely taught by chemistry teachers, and are deceptively difficult for introductory chemistry students to understand. The synthesis of zinc iodide has many scientific advantages over current syntheses of binary compounds from elements such as the syntheses of copper sulfide and magnesium oxide. For example, zinc iodide can be synthesized to 1% of theoretical mass in less than a half an hour and can be readily analyzed qualitatively as well as quantitatively by two different titrations. As a set of reactions, the synthesis and decomposition of zinc iodide is safe to perform, reliable, inexpensive, and does not pose a threat to the environment. The author has developed a small collection of teacher activities describing the synthesis and decomposition of zinc iodide. The activities are innovative because they contain improvements not found in the existing literature. Appropriate for high school and first year college chemistry teachers, all of the activities contain detailed procedures and discussions as well as safety and disposal requirements.

Demeo, Stephen

1995-09-01

268

Massively parallel computation of 3D flow and reactions in chemical vapor deposition reactors  

SciTech Connect

Computer modeling of Chemical Vapor Deposition (CVD) reactors can greatly aid in the understanding, design, and optimization of these complex systems. Modeling is particularly attractive in these systems since the costs of experimentally evaluating many design alternatives can be prohibitively expensive, time consuming, and even dangerous, when working with toxic chemicals like Arsine (AsH{sub 3}): until now, predictive modeling has not been possible for most systems since the behavior is three-dimensional and governed by complex reaction mechanisms. In addition, CVD reactors often exhibit large thermal gradients, large changes in physical properties over regions of the domain, and significant thermal diffusion for gas mixtures with widely varying molecular weights. As a result, significant simplifications in the models have been made which erode the accuracy of the models` predictions. In this paper, the authors will demonstrate how the vast computational resources of massively parallel computers can be exploited to make possible the analysis of models that include coupled fluid flow and detailed chemistry in three-dimensional domains. For the most part, models have either simplified the reaction mechanisms and concentrated on the fluid flow, or have simplified the fluid flow and concentrated on rigorous reactions. An important CVD research thrust has been in detailed modeling of fluid flow and heat transfer in the reactor vessel, treating transport and reaction of chemical species either very simply or as a totally decoupled problem. Using the analogy between heat transfer and mass transfer, and the fact that deposition is often diffusion limited, much can be learned from these calculations; however, the effects of thermal diffusion, the change in physical properties with composition, and the incorporation of surface reaction mechanisms are not included in this model, nor can transitions to three-dimensional flows be detected.

Salinger, A.G.; Shadid, J.N.; Hutchinson, S.A.; Hennigan, G.L.; Devine, K.D.; Moffat, H.K.

1997-12-01

269

Experimental results of exothermic reaction with concentration gradient catalyst in a solar chemical heat pump  

Microsoft Academic Search

A solar chemical heat pump can upgrade low-temperature solar heat of about 80°C to about 150-200°C by using the reversible chemical reactions of 2-propanol\\/acetone\\/hydrogen, which are composed of endothermic and exothermic reactions. In the exothermic process of the above reaction, a temperature peak occurs near the inlet of the reaction zone in the case of uniform catalyst arrangement. Such a

T. Takashima; T. Doi; Y. Ando; T. Tanaka; R. Miyahara; J. Kamoshida

1997-01-01

270

Extended Hartree-Fock theory of chemical reactions. VIII. Hydroxylation reactions by P450  

NASA Astrophysics Data System (ADS)

We have investigated the reaction pathways for the primary hydroxylation reaction of trimethylmethane by a high-valent Fe(IV) dbond O porphyrin pi-cation radical species known as compound I at the B3LYP/CEP-31G level. The isoelectronic analogy of the Fe(IV) dbond O core of compound I to a molecular oxygen (O2) has been successfully used to clarify the important roles of the singlet excited state of the Fe(IV) dbond O core in the alkane hydroxylation, which has hitherto been neglected. The reaction is initiated by the rate-determining hydrogen-atom abstraction from the substrate to give a discrete radical intermediate complex, in accordance with the conventional radical rebound mechanism. Similar to the chemistry of O2, however, one of the singlet excited states, i.e., the diradical component of the 1Delta state of the Fe(IV) dbond O core intercepts the triplet ground state (the 3Sigma state) in the region of the transition state for the hydrogen abstraction. Our findings strongly indicate that the exchange polarization or intersystem crossing for the nonradiative transition to the locally singlet state is highly important to enhance the reactivity of compound I.

Isobe, Hiroshi; Nishihara, Satomichi; Shoji, Mitsuo; Yamanaka, Shusuke; Shimada, Jiro; Hagiwara, Masayuki; Yamaguchi, Kizashi

271

Study on the key problems of interaction between microwave and chemical reaction  

Microsoft Academic Search

Microwave has been found as an efficient heating method in chemical industry. However, in present days the interaction between\\u000a microwave and chemical reactions has not been deeply understood, which restricts a wider application of high power microwave\\u000a in chemical industry. In this paper, the key problems of interaction between microwave and chemical reaction are investigated,\\u000a such as complex effective permittivity

Xiaoqing Yang; Kama Huang

2007-01-01

272

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a novel procedure to speed up the training of NPCA. The same procedure termed L{sub 2}Boost can be used to increase the order of approximation of the Generalized Regression Neural Network (GRNN). It is pointed out that GRNN is a basic procedure for the emerging mesh free CFD. Also reported is an efficient simple approach of computing the derivatives of GRNN function approximation using complex variables or the Complex Step Method (CSM). The results presented demonstrate the significance of the methods developed and will be useful in many areas of applied science and engineering.

Nelson Butuk

2005-12-01

273

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

This is an annual technical report for the work done over the last year (period ending 9/30/2004) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a procedure to speed up the training of NPCA. The developed procedure is based on the non-parametric statistical technique of kernel smoothing. When this smoothing technique is implemented as a Neural Network, It is know as Generalized Regression Neural Network (GRNN). We present results of implementing GRNN on a test problem. In addition, we present results of an in house developed 2-D CFD code that will be used through out the project period.

Nelson Butuk

2004-12-01

274

Continuous chemical reaction chromatography. Progress report, January 1989--January 1992  

SciTech Connect

The past three years have been devoted to investigating simulated countercurrent chomatographic moving bed separators (SCMCS) and simulated countercurrent moving bed reactors (SCMCR). These are novel separators and reactors used for separation, or for carrying out a chemical reaction and separation continuously and simultaneously in fixed bed. In the SCMCR and the SCMCS the process aspects of a countercurrent moving bed, in which a stream of solids flows countercurrent to an inert fluid and past stationary reactant inlet, is simulated by successively switching feed and product take-off streams through a series of inlets located at fixed intervals along a fixed bed or between a series of packed columns. The flow of solids past a fixed feed point, characteristic of countercurrent moving beds, is replaced by motion of the feed past a fixed packed bed. Feed enters a particular column for a fixed length of time, and then is switched to the next column. Product streams are also advanced simultaneously. When the feed point has progressed to the end it is returned to the starting position and the process repeated. The shifting of the feed and the product positions in the direction of fluid flow thus simulates the movement of solids in the opposite direction. The requisite motion between the feed and the bed, which is continuous for true countercurrency, is replaced by periodic, discrete steps in simulated countercurrency. The continuous, steady state operation characteristic of true countercurrency is replaced by periodic transients at each switch of the feed.

Aris, R.; Carr, R.W.

1992-07-01

275

Chemical reactions on rutile TiO2(110).  

PubMed

Understanding the surface chemistry of TiO2 is key to the development and optimisation of many technologies, such as solar power, catalysis, gas sensing, medical implantation, and corrosion protection. In order to address this, considerable research effort has been directed at model single crystal surfaces of TiO2. Particular attention has been given to the rutile TiO2(110) surface because it is the most stable face of TiO2. In this critical review, we discuss the chemical reactivity of TiO2(110), focusing in detail on four molecules/classes of molecules. The selected molecules are water, oxygen, carboxylic acids, and alcohols-all of which have importance not only to industry but also in nature (173 references). PMID:18818830

Lun Pang, Chi; Lindsay, Robert; Thornton, Geoff

2008-09-04

276

Evaluation of reaction mechanism of coal-metal oxide interactions in chemical-looping combustion  

SciTech Connect

The knowledge of reaction mechanism is very important in designing reactors for chemical-looping combustion (CLC) of coal. Recent CLC studies have considered the more technically difficult problem of reactions between abundant solid fuels (i.e. coal and waste streams) and solid metal oxides. A definitive reaction mechanism has not been reported for CLC reaction of solid fuels. It has often been assumed that the solid/solid reaction is slow and therefore requires that reactions be conducted at temperatures high enough to gasify the solid fuel, or decompose the metal oxide. In contrast, data presented in this paper demonstrates that solid/solid reactions can be completed at much lower temperatures, with rates that are technically useful as long as adequate fuel/metal oxide contact is achieved. Density functional theory (DFT) simulations as well as experimental techniques such as thermo-gravimetric analysis (TGA), flow reactor studies, in situ X-ray photo electron spectroscopy (XPS), in situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to evaluate how the proximal interaction between solid phases proceeds. The data indicate that carbon induces the Cu-O bond breaking process to initiate the combustion of carbon at temperatures significantly lower than the spontaneous decomposition temperature of CuO, and the type of reducing medium in the vicinity of the metal oxide influences the temperature at which the oxygen release from the metal oxide takes place. Surface melting of Cu and wetting of carbon may contribute to the solid-solid contacts necessary for the reaction. (author)

Siriwardane, Ranjani; Richards, George; Poston, James [US Department of Energy, National Energy Technology Laboratory, 3610 Collins Ferry Road, P.O. Box 880, Morgantown, WV 26507-0880 (United States); Tian, Hanjing; Miller, Duane; Simonyi, Thomas [US Department of Energy, National Energy Technology Laboratory, 3610 Collins Ferry Road, P.O. Box 880, Morgantown, WV 26507-0880 (United States); URS, 3610 Collins Ferry Road, Morgantown, WV 26505 (United States)

2010-11-15

277

Detailed Chemical Kinetic Reaction Mechanisms for Autoignition of Isomers of Heptane Under Rapid Compression  

SciTech Connect

Detailed chemical kinetic reaction mechanisms are developed for combustion of all nine isomers of heptane (C{sub 7}H{sub 16}), and these mechanisms are tested by simulating autoignition of each isomer under rapid compression machine conditions. The reaction mechanisms focus on the manner in which the molecular structure of each isomer determines the rates and product distributions of possible classes of reactions. The reaction pathways emphasize the importance of alkylperoxy radical isomerizations and addition reactions of molecular oxygen to alkyl and hydroperoxyalkyl radicals. A new reaction group has been added to past models, in which hydroperoxyalkyl radicals that originated with abstraction of an H atom from a tertiary site in the parent heptane molecule are assigned new reaction sequences involving additional internal H atom abstractions not previously allowed. This process accelerates autoignition in fuels with tertiary C-H bonds in the parent fuel. In addition, the rates of hydroperoxyalkylperoxy radical isomerization reactions have all been reduced so that they are now equal to rates of analogous alkylperoxy radical isomerizations, significantly improving agreement between computed and experimental ignition delay times in the rapid compression machine. Computed ignition delay times agree well with experimental results in the few cases where experiments have been carried out for specific heptane isomers, and predictive model calculations are reported for the remaining isomers. The computed results fall into three general groups; the first consists of the most reactive isomers, including n-heptane, 2-methyl hexane and 3-methyl hexane. The second group consists of the least reactive isomers, including 2,2-dimethyl pentane, 3,3-dimethyl pentane, 2,3-dimethyl pentane, 2,4-dimethyl pentane and 2,2,3-trimethyl butane. The remaining isomer, 3-ethyl pentane, was observed computationally to have an intermediate level of reactivity. These observations are generally consistent with knocking tendencies of these isomers, as measured by octane ratings, although the correlations are only approximate.

Westbrook, C K; Pitz, W J; Boercker, J E; Curran, H J; Griffiths, J F; Mohamed, C; Ribaucour, M

2001-12-17

278

The chemical evolution of the Galaxy: the importance of stars with an initial mass larger  

Microsoft Academic Search

In the present paper we investigate in how far stars with an initial mass larger than 40M? affect the chemical enrichment of the Galaxy. We illustrate the importance for chemical yields of a most up to date treatment of the various stellar wind mass loss episodes in stellar evo- lutionary codes and we discuss the effects of a possible supernova-like

E. De Donder; D. Vanbeveren

279

Chemical Processes in Protoplanetary Disks. II. On the Importance of Photochemistry and X-Ray Ionization  

NASA Astrophysics Data System (ADS)

We investigate the impact of photochemistry and X-ray ionization on the molecular composition of, and ionization fraction in, a protoplanetary disk surrounding a typical T Tauri star. We use a sophisticated physical model, which includes a robust treatment of the radiative transfer of UV and X-ray radiation, and calculate the time-dependent chemical structure using a comprehensive chemical network. In previous work, we approximated the photochemistry and X-ray ionization; here, we recalculate the photoreaction rates using the explicit UV wavelength spectrum and wavelength-dependent reaction cross sections. We recalculate the X-ray ionization rate using our explicit elemental composition and X-ray energy spectrum. We find that photochemistry has a larger influence on the molecular composition than X-ray ionization. Observable molecules sensitive to the photorates include OH, HCO+, N2H+, H2O, CO2, and CH3OH. The only molecule significantly affected by the X-ray ionization is N2H+, indicating that it is safe to adopt existing approximations of the X-ray ionization rate in typical T Tauri star-disk systems. The recalculation of the photorates increases the abundances of neutral molecules in the outer disk, highlighting the importance of taking into account the shape of the UV spectrum in protoplanetary disks. A recalculation of the photoreaction rates also affects the gas-phase chemistry due to the adjustment of the H/H2 and C+/C ratios. The disk ionization fraction is not significantly affected by the methods adopted to calculate the photochemistry and X-ray ionization. We determine that there is a probable "dead zone" where accretion is suppressed, present in a layer, Z/R <~ 0.1-0.2, in the disk midplane, within R ? 200 AU.

Walsh, Catherine; Nomura, Hideko; Millar, T. J.; Aikawa, Yuri

2012-03-01

280

A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions  

NASA Astrophysics Data System (ADS)

This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing NE equilibrium reactions and a set of reactive transport equations of M NE kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C.; Brooks, Scott C.; Pace, Molly N.; Kim, Young-Jin; Jardine, Philip M.; Watson, David B.

2007-06-01

281

Systematic exploration of the mechanism of chemical reactions: the global reaction route mapping (GRRM) strategy using the ADDF and AFIR methods.  

PubMed

Global reaction route mapping (GRRM), a fully-automated search for all important reaction pathways relevant to a given purpose, on the basis of quantum chemical calculations enables systematic elucidation of complex chemical reaction mechanisms. However, GRRM had previously been limited to very simple systems. This is mainly because such calculations are highly demanding even in small systems when a brute-force sampling is considered. Hence, we have developed two independent but complementary methods: anharmonic downward distortion following (ADDF) and artificial force induced reaction (AFIR) methods. ADDF can follow reaction pathways starting from local minima on the potential energy surface (PES) toward transition structures (TSs) and dissociation channels. AFIR can find pathways starting from two or more reactants toward TSs for their associative reactions. In other words, ADDF searches for A ? X type isomerization and A ? X + Y type dissociation pathways, whereas AFIR finds A + B ? X (+ Y) type associative pathways. Both follow special paths called the ADDF path and the AFIR path, and these tend to pass through near TSs of corresponding reaction pathways, giving approximate TSs. Such approximate TSs can easily be re-optimized to corresponding true TSs by standard geometry optimizations. On the basis of these two methods, we have proposed practical strategies of GRRM. The GRRM strategies have been applied to a variety of chemical systems ranging from thermal- and photochemical-reactions in small systems to organometallic- and enzyme-catalysis, on the basis of quantum chemical calculations. In this perspective, we present an overview of the GRRM strategies and some results of applications. Their practical usage for systematic prediction is also discussed. PMID:23389653

Maeda, Satoshi; Ohno, Koichi; Morokuma, Keiji

2013-03-21

282

Fatty acid oxidation in anoxic marine sediments: the importance of hydrogen sensitive reactions  

Microsoft Academic Search

In anoxic marine sediments fatty acids may be oxidized directly by sulfate reducing bacteria, or may be oxidized by pathways which result in hydrogen production. Some of these latter reactions are quite sensitive to hydrogen concentrations ... in other words if hydrogen concentrations become elevated, fatty acid oxidation will cease. Thus sulfate reducers may actually play two important roles in

Matthew A. Monetti; Mary I. Scranton

1992-01-01

283

Patchy Reaction?Diffusion and Population Abundance: The Relative Importance of Habitat Amount and Arrangement  

Microsoft Academic Search

A discrete reaction-diffusion model was used to estimate long-term equilibrium populations of a hypothetical species inhab- iting patchy landscapes to examine the relative importance of habitat amount and arrangement in explaining population size. When ex- amined over a broad range of habitat amounts and arrangements, population size was largely determined by a pure amount effect (pro- portion of habitat in

Michael Bevers

2002-01-01

284

Detection of a wide range of medically important fungi by the polymerase chain reaction  

Microsoft Academic Search

Summary. A polymerase chain reaction (PCR) method was developed that was capable of detecting a wide range of medically important fungi from clinical specimens. The primer pair was designed in conserved sequences of 1 8s-ribosomal RNA genes shared by most fungi. The lower limit of detection of this PCR technique was 1 pg of Cundidu ulbicans genomic DNA by ethidium

K. Makimura; SOMAY Y. MURAYAMA; H. Yamaguchi

1994-01-01

285

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the significant development made in developing a truly meshfree computational fluid dynamics (CFD) flow solver to be coupled to NPCA. First, the procedure of obtaining nearly analytic accurate first order derivatives using the complex step method (CSM) is extended to include computation of accurate meshfree second order derivatives via a theorem described in this report. Next, boosted generalized regression neural network (BGRNN), described in our previous report is combined with CSM and used to obtain complete solution of a hard to solve wave dominated sample second order partial differential equation (PDE): the cubic Schrodinger equation. The resulting algorithm is a significant improvement of the meshfree technique of smooth particle hydrodynamics method (SPH). It is suggested that the demonstrated meshfree technique be termed boosted smooth particle hydrodynamics method (BSPH). Some of the advantages of BSPH over other meshfree methods include; it is of higher order accuracy than SPH; compared to other meshfree methods, it is completely meshfree and does not require any background meshes; It does not involve any construction of shape function with their associated solution of possibly ill conditioned matrix equations; compared to some SPH techniques, no equation for the smoothing parameter is required; finally it is easy to program.

Nelson Butuk

2006-09-21

286

Heat-of-Reaction Chemical Heat Pumps: Possible Configurations.  

National Technical Information Service (NTIS)

Chemical heat pumps utilize working fluids which undergo reversible chemical changes. Mechanically driven reactive heat pump cycles or, alternatively, heat driven heat pumps in which either heat engine or heat pump working fluid is reactive, are considere...

L. D. Kirol

1986-01-01

287

CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

288

Method of operating a thermal engine powered by a chemical reaction  

DOEpatents

The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction. 7 figs.

Ross, J.; Escher, C.

1988-06-07

289

Motivational Factors Contributing to Turkish High School Students' Achievement in Gases and Chemical Reactions  

ERIC Educational Resources Information Center

|This study aimed to investigate the contribution of motivational factors to 10th grade students' achievement in gases and chemical reactions in chemistry. Three hundred fifty nine 10th grade students participated in the study. The Gases and Chemical Reactions Achievement Test and the Motivated Strategies for Learning Questionnaire were…

Kadioglu, Cansel; Uzuntiryaki, Esen

2008-01-01

290

Stochastic simulation of chemical reactions with spatial resolution and single molecule detail  

Microsoft Academic Search

Methods are presented for simulating chemical reaction networks with a spatial resolution that is accurate to nearly the size scale of individual molecules. Using an intuitive picture of chemical reaction systems, each molecule is treated as a point-like particle that diffuses freely in three-dimensional space. When a pair of reactive molecules collide, such as an enzyme and its substrate, a

Steven S. Andrews; Dennis Bray

2004-01-01

291

Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols  

ERIC Educational Resources Information Center

|Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the…

Goodney, David E.

2006-01-01

292

Micromechanical modeling of shock-induced chemical reactions in heterogeneous multi-material powder mixtures  

Microsoft Academic Search

Shock waves create a unique environment of high pressure, temperature, strain rate, and gradients thereof. Chemical reactions that occur in this regime can lead to the synthesis of new materials that are not possible under conventional conditions. Shock-induced chemical reactions (also known as shock synthesis) is difficult to study experimentally due to the small time and space scales over which

Ian P. H. Do; David J. Benson

2001-01-01

293

Introducing Stochastic Simulation of Chemical Reactions Using the Gillespie Algorithm and MATLAB: Revisited and Augmented  

ERIC Educational Resources Information Center

|The stochastic simulation of chemical reactions, specifically, a simple reversible chemical reaction obeying the first-order, i.e., linear, rate law, has been presented by Martinez-Urreaga and his collaborators in this journal. The current contribution is intended to complement and augment their work in two aspects. First, the simple reversible…

Argoti, A.; Fan, L. T.; Cruz, J.; Chou, S. T.

2008-01-01

294

Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction  

ERIC Educational Resources Information Center

|Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

Tellinghuisen, Joel

2006-01-01

295

Comparison of designed and randomly generated catalysts for simple chemical reactions  

PubMed Central

There has been recent success in designing enzymes for simple chemical reactions using a two-step protocol. In the first step, a geometric matching algorithm is used to identify naturally occurring protein scaffolds at which predefined idealized active sites can be realized. In the second step, the residues surrounding the transition state model are optimized to increase transition state binding affinity and to bolster the primary catalytic side chains. To improve the design methodology, we investigated how the set of solutions identified by the design calculations relate to the overall set of solutions for two different chemical reactions. Using a TIM barrel scaffold in which catalytically active Kemp eliminase and retroaldolase designs were obtained previously, we carried out activity screens of random libraries made to be compositionally similar to active designs. A small number of active catalysts were found in screens of 103 variants for each of the two reactions, which differ from the computational designs in that they reuse charged residues already present in the native scaffold. The results suggest that computational design considerably increases the frequency of catalyst generation for active sites involving newly introduced catalytic residues, highlighting the importance of interaction cooperativity in enzyme active sites.

Kipnis, Yakov; Baker, David

2012-01-01

296

Probing Isotope Effects in Chemical Reactions Using Single Ions  

SciTech Connect

Isotope effects in reactions between Mg{sup +} in the 3p {sup 2}P{sub 3/2} excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only {approx}250 reactions with HD, the branching ratio between formation of MgD{sup +} and MgH{sup +} is found to be larger than 5. From an additional 65 reactions with H{sub 2} and D{sub 2} we find that the overall fragmentation probability of the intermediate MgH{sub 2}{sup +}, MgHD{sup +}, or MgD{sub 2}{sup +} complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.

Staanum, Peter F.; Hoejbjerre, Klaus; Drewsen, Michael [QUANTOP - Danish National Research Foundation Centre for Quantum Optics, University of Aarhus, 8000 Aarhus (Denmark); Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus (Denmark); Wester, Roland [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg (Germany)

2008-06-20

297

Polarization of molecular angular momentum in the chemical reactions Li + HF and F + HD  

NASA Astrophysics Data System (ADS)

The quantum mechanical approach to vector correlation of angular momentum orientation and alignment in chemical reactions [G. Balint-Kurti and O. S. Vasyutinskii, J. Phys. Chem. A 113, 14281 (2009)] is applied to the molecular reagents and products of the Li + HF [L. Gonzalez-Sanchez, O. S. Vasyutinskii, A. Zanchet, C. Sanz-Sanz, and O. Roncero, Phys. Chem. Chem. Phys. 13, 13656 (2011)] and F + HD [D. De Fazio, J. Lucas, V. Aquilanti, and S. Cavalli, Phys. Chem. Chem. Phys. 13, 8571 (2011)] reactions for which accurate scattering information has become recently available through time-dependent and time-independent approaches. Application of the theory to two important particular cases of the reactive collisions has been considered: (i) the influence of the angular momentum polarization of reactants in the entrance channel on the spatial distribution of the products in the exit channel and (ii) angular momentum polarization of the products of the reaction between unpolarized reactants. In the former case, the role of the angular momentum alignment of the reactants is shown to be large, particularly when the angular momentum is perpendicular to the reaction scattering plane. In the latter case, the orientation and alignment of the product angular momentum was found to be significant and strongly dependent on the scattering angle. The calculation also reveals significant differences between the vector correlation properties of the two reactions under study which are due to difference in the reaction mechanisms. In the case of F + HD reaction, the branching ratio between HF and DF production points out interest in the insight gained into the detailed dynamics, when information is available either from exact quantum mechanical calculations or from especially designed experiments. Also, the geometrical arrangement for the experimental determination of the product angular momentum orientation and alignment based on a compact and convenient spherical tensor expression for the intensity of the resonance enhanced multiphoton ionization (REMPI 2 + 1) signal is suggested.

Krasilnikov, Mikhail B.; Popov, Ruslan S.; Roncero, Octavio; De Fazio, Dario; Cavalli, Simonetta; Aquilanti, Vincenzo; Vasyutinskii, Oleg S.

2013-06-01

298

Polarization of molecular angular momentum in the chemical reactions Li + HF and F + HD.  

PubMed

The quantum mechanical approach to vector correlation of angular momentum orientation and alignment in chemical reactions [G. Balint-Kurti and O. S. Vasyutinskii, J. Phys. Chem. A 113, 14281 (2009)] is applied to the molecular reagents and products of the Li + HF [L. Gonzalez-Sanchez, O. S. Vasyutinskii, A. Zanchet, C. Sanz-Sanz, and O. Roncero, Phys. Chem. Chem. Phys. 13, 13656 (2011)] and F + HD [D. De Fazio, J. Lucas, V. Aquilanti, and S. Cavalli, Phys. Chem. Chem. Phys. 13, 8571 (2011)] reactions for which accurate scattering information has become recently available through time-dependent and time-independent approaches. Application of the theory to two important particular cases of the reactive collisions has been considered: (i) the influence of the angular momentum polarization of reactants in the entrance channel on the spatial distribution of the products in the exit channel and (ii) angular momentum polarization of the products of the reaction between unpolarized reactants. In the former case, the role of the angular momentum alignment of the reactants is shown to be large, particularly when the angular momentum is perpendicular to the reaction scattering plane. In the latter case, the orientation and alignment of the product angular momentum was found to be significant and strongly dependent on the scattering angle. The calculation also reveals significant differences between the vector correlation properties of the two reactions under study which are due to difference in the reaction mechanisms. In the case of F + HD reaction, the branching ratio between HF and DF production points out interest in the insight gained into the detailed dynamics, when information is available either from exact quantum mechanical calculations or from especially designed experiments. Also, the geometrical arrangement for the experimental determination of the product angular momentum orientation and alignment based on a compact and convenient spherical tensor expression for the intensity of the resonance enhanced multiphoton ionization (REMPI 2 + 1) signal is suggested. PMID:23822239

Krasilnikov, Mikhail B; Popov, Ruslan S; Roncero, Octavio; De Fazio, Dario; Cavalli, Simonetta; Aquilanti, Vincenzo; Vasyutinskii, Oleg S

2013-06-28

299

Chemical modeling of irreversible reactions in nuclear waste-water-rock systems  

SciTech Connect

Chemical models of aqueous geochemical systems are usually built on the concept of thermodynamic equilibrium. Though many elementary reactions in a geochemical system may be close to equilibrium, others may not be. Chemical models of aqueous fluids should take into account that many aqueous redox reactions are among the latter. The behavior of redox reactions may critically affect migration of certain radionuclides, especially the actinides. In addition, the progress of reaction in geochemical systems requires thermodynamic driving forces associated with elementary reactions not at equilibrium, which are termed irreversible reactions. Both static chemical models of fluids and dynamic models of reacting systems have been applied to a wide spectrum of problems in water-rock interactions. Potential applications in nuclear waste disposal range from problems in geochemical aspects of site evaluation to those of waste-water-rock interactions. However, much further work in the laboratory and the field will be required to develop and verify such applications of chemical modeling.

Wolery, T.J.

1981-02-01

300

Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes  

NASA Astrophysics Data System (ADS)

In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge, incorporating dynamic aspects of chemical processes, linking a visualization to the associated chemical phenomenon, and connecting between the visualization and chemistry concepts. We also compared students who were able to create dynamic visualizations with those who only created static visualizations. The results indicated a relationship between students constructing a dynamic view of chemical reaction processes and their understanding of chemical reactions. This study provides insights into the use of visualizations to support instruction and assessment to facilitate students' integrated understanding of chemical reactions.

Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

2013-09-01

301

Chemical reaction model for oil and gas generation from type 1 and type 2 kerogen  

SciTech Connect

A global model for the generation of oil and gas from petroleum source rocks is presented. The model consists of 13 chemical species and 10 reactions, including an alternate-pathway mechanism for kerogen pyrolysis. Reaction rate parameters and stoichiometry coefficients determined from a variety of pyrolysis data are given for both type I and type II kerogen. Use of the chemical reaction model is illustrated for typical geologic conditions.

Braun, R.L.; Burnham, A.K.

1993-06-01

302

Chemical reaction of SiCp\\/Al composites during multiple remelting  

Microsoft Academic Search

In the present study, the chemical reaction of SiCp\\/Al composites during multiple remelting above the liquidus was investigated using Differential Scanning Calorimetry and Transmission Electron Microscope. The experimental results indicated that the chemical reaction of SiC particles increased with increasing remelting temperature and the number of recycling runs. After reaching a certain degree of reaction, no further change occurred during

Tongxiang Fan; Di Zhang; Guang Yang; Toshiya Shibayanagi; Masaaki Naka; Takao Sakata; Hirotaro Mori

2003-01-01

303

Chemical reaction process and the single crystal growth of CuInS 2 compound  

Microsoft Academic Search

In order to establish the preparation method of high-quality CuInS2 single crystals, we have investigated the chemical reaction process by means of differential thermal analysis and powder X-ray diffraction measurements. In the chemical reaction process of a Cu+In+2S mixture, an explosive exothermic reaction occurs at 640°C, which is ascribed to the formation of products of the In–S system. In the

Hiroaki Matsushita; Tomohiro Mihira; Takeo Takizawa

1999-01-01

304

Variational principles for describing chemical reactions: Condensed reactivity indices  

NASA Astrophysics Data System (ADS)

Two recent papers [P. W. Ayers and R. G. Parr, J. Am. Chem. Soc. 122, 2010 (2000); 123, 2007 (2001)] have shown how variational principles for the energy may be used to derive and elucidate the significance of the chemical reactivity indices of density-functional theory. Here, similar ideas are applied, yielding a systematic, mathematically rigorous, and physically sound approach to condensed reactivity indices. First, we use the variational principle for the energy to derive an expression for the condensed Fukui function index in terms of the condensed hardness kernel. Next, we address an important open problem pertaining to condensed reactivity indices: when (if ever) is the condensed Fukui function for an atom in a molecule negative? In particular, our analysis confirms the observation, hitherto based only on computational evidence, that the Hirshfeld partitioning is optimal for obtaining non-negative Fukui functions. We also hypothesize that the strong diagonal dominance of the condensed hardness kernel is sufficient for the non-negativity of the Fukui function. Errors in the partitioning of molecules into atoms and inadequate treatment of correlation are pinpointed as the most likely causes of negative condensed Fukui functions. We conclude by noting that the condensed Fukui functions are, in some respects, more appropriate indicators of a molecular site's reactivity than the Fukui function itself.

Ayers, Paul W.; Morrison, Robert C.; Roy, Ram K.

2002-05-01

305

Characterization of chemically modified hyperthermophilic enzymes for chemical syntheses and bioremediation reactions. 1998 annual progress report  

SciTech Connect

'Remediation processes frequently involve species possessing limited solubility in water. The authors are interested in novel strategies that use molecularly-engineered enzymes with enhanced activity and stability for the remediation of recalcitrant compounds in organic media. Organic biocatalysis may be motivated by the nature of the substrate itself, or by augmented mass transport, ease of product recovery, or novel reaction pathways afforded by the organic solvent. However, naturally-occurring enzymes are usually subject to quite limited activity and stability in such organic environments. The objective of the current work is to gain a fundamental understanding of the molecular and catalytic properties of enzymes that have been chemically-modified so that they are catalytically-active and chemically-thermally-stable in organic solvents. The premise for this study is that highly stable enzymes which are catalytically active in both water and in a range of organic solvents are optimally suited for bioremediation where substrates of interest are more soluble and may be processed with greater specificity in nonaqueous solvents. This bioprocessing system will be assessed using PCB''s, DNAPL''s and PAH''s. As of the second of year of a 3-year project, the authors have obtained promising results for both the demonstration of the proposed remediation strategy and fundamental understanding of the enzymatic catalysis in organic media. In one of the efforts, ligninase (LiP) was modified by poly(ethylene glycol) (PEG) and examined for the degradation of pentachlorophenol (PCP) in water-solvent mixtures. In the other efforts, basic catalytic behaviors of the chemically modified hyperthermophilic metalloenzymes including ferredoxin, hydrogenase and aldehyde oxidoreductase were examined in organic solvents.'

Kaufman, E.N. [Oak Ridge National Lab., TN (US); Adams, M.W.W. [Univ. of Georgia, Athens, GA (US)

1998-06-01

306

A Unified Approach to the Study of Chemical Reactions in Freshman Chemistry.  

ERIC Educational Resources Information Center

|Provides rationale and objectives for presenting chemical reactions in a unified, logical six-stage approach rather than a piecemeal approach. Stages discussed include: introduction, stable electronic configurations and stable oxidation states, reactions between two free elements, ion transfer/proton transfer reactions, double displacement…

Cassen, T.; DuBois, Thomas D.

1982-01-01

307

Transition State Spectroscopy of Bimolecular Chemical Reactions. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

One of the fundamental goals of chemical physics has been to understand the nature of the potential energy surfaces on which chemical reactions occur. Much of this interest focuses on the transition state region: the region of the surface where chemical b...

D. M. Neumark

1992-01-01

308

Statistical mechanical modelling of chemical reactions in complex systems: the kinetics of the Haem carbon monoxide binding–unbinding reaction in Myoglobin  

Microsoft Academic Search

The free energy profile and the (classical) kinetics of chemical reactions in (soft) condensed phase may be well modelled\\u000a theoretically by means of molecular dynamics simulations, the perturbed matrix method (PMM) and statistical mechanics, as\\u000a we provided in previous articles. In this paper, we describe the theoretical framework, discussing thoroughly its crucial\\u000a points, and apply the model to an important

Andrea Amadei; Marco D’Abramo; Isabella Daidone; Maira D’Alessandro; Alfredo Di Nola; Massimiliano Aschi

2007-01-01

309

The canonical and other mechanisms of elementary chemical reactions.  

PubMed

This article introduces a definition of the concept of elementary reaction mechanism that, while conforming to the traditional view of reaction mechanisms as dynamical processes whereby reagents are transformed into products, sharpens it by requiring reagent and product states to be completely specified and fully correlated. This leads to well-defined mathematical requirements for classification of a dynamical process as a reaction mechanism and also to a straightforward mathematical procedure for the determination of a special class of independent collision mechanisms that are dubbed "canonical". Canonical mechanisms result from an exact decomposition of the differential cross section of the reaction and form a complete orthogonal basis in terms of which all reaction mechanisms can be described. Examples involving the benchmark F + H2 and D + H2 reactions at energies ranging from ultralow to hyperthermal illustrate how canonical and other reaction mechanisms can be visualised and also how analysis of a reaction in terms of its canonical mechanisms can provide insight into its dynamics. PMID:19462575

Aldegunde, Jesús; Aoiz, F Javier; Sáez-Rábanos, Vicente; Kendrick, Brian K; de Miranda, Marcelo P

2007-11-21

310

Chemical reaction engineering: A multiscale approach to a multiobjective task  

Microsoft Academic Search

A strategy for synthesizing a reaction system to meet various business and technical objectives is outlined. It replaces the conventional paradigm — the sequential evolution of the microreactor, bench-scale reactor, pilot plant reactor and commercial reactor. Starting with a reaction proposed for commercialization, this approach examines the synthesis problem from the viewpoint of the plant, the reactor, hydrodynamics, transport phenomena,

Jan J. Lerou; Ka M. Ng

1996-01-01

311

Nanoscale Pattern Formation in Non-Equilibrium Surface Chemical Reactions  

Microsoft Academic Search

Using examples from surface science, we consider in this article problems of non- equilibrium pattern formation in reactive soft matter. An interplay of reaction, diffusion and energetic interactions between adatoms can produce a variety of non-equilibrium nanos- tructures, both stationary and traveling. These structures are similar to the patterns found in phase-separating binary mixtures under the influence of reactions. Because

Y. De Decker; A. S. Mikhailov

2006-01-01

312

CHEMICAL REACTIONS OF AQUATIC HUMIC MATERIALS WITH SELECTED OXIDANTS  

EPA Science Inventory

A study was conducted to identify the specific organic reaction products of natural aquatic humic materials with selected oxidants (KMnO4, HOCl, Cl02, O3 and monochloramine). Reaction products were identified by GC/MS after solvent extraction and derivatization. The two most reac...

313

Hot carrier-selective chemical reactions on Ag(110)  

NASA Astrophysics Data System (ADS)

Here, we show that the pathways, products, and efficiencies of reactions occurring on a metal surface can be spatially modulated by varying the type and energy of hot carriers produced by injecting tunneling electrons or holes from a scanning tunneling microscope tip into the metal surface. Control over the metal surface reactions was demonstrated for the large-scale dissociation reaction of O2 molecules on a Ag(110) surface. Hot electrons (or holes) transported through the metal surface to chemisorbed O2 selectively dissociated the molecule into two oxygen atoms separated along the [110] (or [001]) lattice direction. The reaction selectivity was enhanced compared to the selectivity of a direct reaction involving tunneling carriers.

Hahn, Jae Ryang; Jang, Sang Hoon; Kim, Ki Wan; Son, Seung Bae

2013-08-01

314

Magnetic and other field effects on prochiral chemical reactions  

NASA Astrophysics Data System (ADS)

Experiments are reported in which three prochiral organic reactions were conducted in the presence of a ca. 1T magnetic field which was oriented with reference to the earth's geometric axes. The sign and magnitude of the rotation varied with the macroscopic orientation of the magnetic field and the time that the reaction was performed. Control measurements were in accord with expectations. The fact that the sign of the observed optical rotation of the product was reversed for all three reported reactions when the magnetic field was reversed for reactions conducted on the same day suggests that either the observed asymmetric synthesis was due to the reactions being conducted in a chiral physical field or extremely unusual stochastic processes were involved.

Piotrowska, Krystyna; Edwards, Deborah; Mitch, Alan; Dougherty, Ralph C.

1980-09-01

315

NEURAL - a tracking detector for neutron-induced reactions of astrophysical importance  

NASA Astrophysics Data System (ADS)

Observations from gamma ray telescopes indicate that most of the galactic 26Al originates in massive stars. Several sites have been discussed for its production, including proton burning in the winds of very massive stars, and the later, explosive burning stages of these stars. Observations from the RHESSI and INTEGRAL missions currently seem to point to the latter scenario. In the advanced burning stages of massive stars the presence of neutrons becomes an important factor in nuclear reaction networks, so in addition to the 26Al(p,?)27Si reaction the neutron capture reactions 26Al(n,p)26Mg and 26Al(n,?)23Na can lead to the destruction of 26Al, and thus alter the observed 26Al abundance. NEURAL is a detector design to measure the excitation functions of these reactions over a wide range of energies. 26Al targets implanted at TRIUMF will be exposed to a pulsed neutron beam at the neutron time-of-flight facility at LANSCE (Los Alamos Neutron Science CEnter). NEURAL is designed to detect all charged reaction products, combining a time projection chamber for the heavy ions, and Si detectors for the light particles mounted around the target. A first prototype has been built and partially tested at TRIUMF and LANSCE in December 2009.

Martin, L.; Buchmann, L.; Carpino, J. F.; Chen, A.; Couture, A.; Davids, B.; Fallis, J.; Fox, S. P.; Hager, U.; Hussein, A.; Laird, A. M.; Olchanski, K.; Ottewell, D.; Ruiz, C.; Ruprecht, G.; Sheffer, G.; Sjue, S.; Tengblad, O.; Tovesson, F.

2011-09-01

316

Classification of chemical substances, reactions, and interactions: The effect of expertise  

NASA Astrophysics Data System (ADS)

This project explored the strategies that undergraduate and graduate chemistry students engaged in when solving classification tasks involving microscopic (particulate) representations of chemical substances and microscopic and symbolic representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention while classifying, identifying the patterns of reasoning that they follow, and comparing the performance of students with different levels of preparation in the discipline. In general, our results suggest that advanced levels of expertise in chemical classification do not necessarily evolve in a linear and continuous way with academic training. Novice students had a tendency to reduce the cognitive demand of the task and rely on common-sense reasoning; they had difficulties differentiating concepts (conceptual undifferentiation) and based their classification decisions on only one variable (reduction). These ways of thinking lead them to consider extraneous features, pay more attention to explicit or surface features than implicit features and to overlook important and relevant features. However, unfamiliar levels of representations (microscopic level) seemed to trigger deeper and more meaningful thinking processes. On the other hand, expert students classified entities using a specific set of rules that they applied throughout the classification tasks. They considered a larger variety of implicit features and the unfamiliarity with the microscopic level of representation did not affect their reasoning processes. Consequently, novices created numerous small groups, few of them being chemically meaningful, while experts created few but large chemically meaningful groups. Novices also had difficulties correctly classifying entities in chemically meaningful groups. Finally, expert chemists in our study used classification schemes that are not necessarily traditionally taught in classroom chemistry (e.g. the structure of substances is more relevant to them than their composition when classifying substances as compounds or elements). This result suggests that practice in the field may develop different types of knowledge framework than those usually presented in chemistry textbooks.

Stains, Marilyne Nicole Olivia

317

A Representation to Apply Usual Data Mining Techniques to Chemical Reactions  

Microsoft Academic Search

\\u000a Chemical reactions always involve several molecules of two types, reactants and products. Existing data mining techniques,\\u000a eg. Quantitative Structure Activity Relationship (QSAR) methods, deal with individual molecules only. In this article, we\\u000a propose to use Condensed Graph of Reaction (CGR) approach merging all molecules involved in a reaction into one molecular\\u000a graph. This allows one to consider reactions as pseudo-molecules

Frank Hoonakker; Nicolas Lachiche; Alexandre Varnek; Alain Wagner

2010-01-01

318

Phase and chemical equilibria in the transesterification reaction of vegetable oils with supercritical lower alcohols  

Microsoft Academic Search

Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters,\\u000a participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic\\u000a parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification\\u000a reaction of free fatty acids and the transesterification reaction

V. I. Anikeev; D. A. Stepanov; A. Ermakova

2011-01-01

319

RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics  

NASA Astrophysics Data System (ADS)

We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions.

Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

2013-03-01

320

The US Export-Import Bank: No evidence of financing restricted chemical exports to Iraq  

SciTech Connect

The authors have reviewed U.S. Export-Import Bank (Eximbank) transactions involving chemicals exported to Iraq from January 1987 to August 1990. Specifically, the authors examined (1) whether there was any evidence that the Eximbank financed the export of dual-use chemicals to Iraq and (2) what the Eximbank`s role was in monitoring and controlling chemical exports. Results are based primarily on a review of documents provided to them by the Eximbank. They did not verify the Eximbank data or corroborate it with the records of the banks or exporters involved in the transactions. There was no evidence in the documents they reviewed to suggest that the Eximbank financed the export of dual-use chemicals (chemicals with both commercial and military applications that could be used for chemical weapons) -- as defined by the Department of Commerce -- to Iraq between January 1987 and August 1990. There were approximately 190 transactions between Iraq and the Eximbank during this period. They focused their review on the eight transactions involving pesticides and related products. The Eximbank has no responsibility or authority for monitoring or controlling the export of chemicals or any other commodities: the Departments of Commerce and State and the US Customs Service share those responsibilities. Nevertheless, the Eximbank has recently developed specific procedures to review applications for financing chemical exports. However, such procedures were not in place when the Eximbank approved the applications for seven of eight pesticide transactions that occurred between January 1987 and August 1990.

Mendelowitz, A.I.; Watson, J.E.; Wood, S.E.; Logan, D.L.; Hinojosa, S.L.

1991-09-01

321

Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.  

SciTech Connect

This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2009-08-01

322

A simple model for two competing chemical reactions  

NASA Astrophysics Data System (ADS)

We study a competitive reaction model in one dimension with different reactivity weights for the reactions. We consider the A + A ? A2 auto-catalytic reaction model and the A + B ? AB monomer monomer reaction model, where A and B are monomers arriving at the surface with probabilities yA and yB, respectively. The model is studied in the site and pair mean field approximations, and by Monte Carlo simulations. The phase diagram of the model displays a line of continuous phase transitions between active and poisoned states, and we determined the critical exponents, ? and ?? of the model. Our results indicate that the critical behavior of the model does not change with the reactivity rate, and it belongs to the directed percolation universality class.

da Costa, E. C.; Figueiredo, W.

2005-12-01

323

Extended transition-state theory and constant-energy chemical-reaction molecular-dynamics method for liquid-phase chemical reactions  

Microsoft Academic Search

An extension of transition-state theory for liquid-phase chemical reactions is presented. The effect of adding a second solvent water molecule on the proton-transfer reaction in a formamidine–water (FW) cluster was studied. Abinitio molecular-orbital calculations were performed for the formamidine–water–water (FWW) system to obtain the adiabatic potential-energy surface. It was expressed in two coordinate systems: (i) the total normal-coordinate system of

Masataka Nagaoka; Yoshishige Okuno; Tokio Yamabe

1992-01-01

324

Innovative processing of porous and cellular materials by chemical reaction  

Microsoft Academic Search

Nickel aluminide foam and porous Ti composite (TiC,TiB(2)\\/Ti) were synthesized. A reaction between Ni and Al was used to make the nickel aluminide foam. Porous Ti composite was fabricated by reactions between (1) Ti and C or (2) Ti and B4C. Gas release from the elemental powders and initial porosity in the green powder compact were the formation mechanisms of

N. Kanetake; M. Kobashi

2006-01-01

325

Nanoscale Pattern Formation in Non-Equilibrium Surface Chemical Reactions  

Microsoft Academic Search

Using examples from surface science, we consider in article problems of non-equilibrium pattern formation in reactive soft matter. An interplay of reaction, diffusion and energetic interactions between adatoms can produce a variety of non-equilibrium nanostructures, both stationary and traveling. These structures are similar to the patterns found in phase-separating binary mixtures under the influence of reactions. Because of their small

Y. D. Decker; A. S. Mikhailov

2006-01-01

326

CFD Analysis of Personal Ventilation with Volumetric Chemical Reactions  

Microsoft Academic Search

This article studies the concentration distribution in the microenvironment of a person and inhalation exposure in a typical office space when modeling first- and second-order reactions. First, wall adsorption of ozone and d-limonene and the resulting volumetric reaction are validated, and 2D computational concentration profiles are compared to the experimental results from Ito (2007b) with reasonable agreement. The validated model

Jackie Russo; H. Ezzat Khalifa

2010-01-01

327

Investigation of chemical reactions in solution using API-MS  

Microsoft Academic Search

The general concepts, advantages, and applications of on-line and off-line screening to organic reaction mechanistic studies applying API-MS are reviewed. An overview is presented of the development and the present stage of connected microreactors to API ion-sources. Examples of the successful application of API in revealing, elucidating, and helping to consolidate several proposed mechanisms of organic reactions are summarized. Finally,

Leonardo Silva Santos; Larissa Knaack; Jürgen O. Metzger

2005-01-01

328

The Fluctuation Theorem in Stochastic Chemical Reaction Systems  

NASA Astrophysics Data System (ADS)

In this study, we consider a simple discrete model of isomerization-type reaction, which can be described in Markovian kinetics. Then we investigate the validity of FT in that model by using the Gillespie method which gives an ensemble of stochastic paths of successive reactions explicitly. We obtain a result that the validity of the FT is determined by time-scale of the dynamics.

Akuzawa, Naohiro; Akimoto, Mitsuhiro

2008-02-01

329

The Bergman reaction of dynemicin A – a quantum chemical investigation  

Microsoft Academic Search

For the first time, the Bergman reaction of a naturally occurring enediyne, namely dynemicin A, is fully investigated at the DFT level of theory using the B3LYP hybrid functional and VDZ basis sets. The calculated geometry of dynemicin A agrees well with the X-ray structure of deoxydynemicin A. The activation barrier is calculated to be 19.4 kcal\\/mol, while the reaction

Bodil Ahlström; Elfi Kraka; Dieter Cremer

2002-01-01

330

Quantum chemical modeling of enzymatic reactions: the case of histone lysine methyltransferase.  

PubMed

Quantum chemical cluster models of enzyme active sites are today an important and powerful tool in the study of various aspects of enzymatic reactivity. This methodology has been applied to a wide spectrum of reactions and many important mechanistic problems have been solved. Herein, we report a systematic study of the reaction mechanism of the histone lysine methyltransferase (HKMT) SET7/9 enzyme, which catalyzes the methylation of the N-terminal histone tail of the chromatin structure. In this study, HKMT SET7/9 serves as a representative case to examine the modeling approach for the important class of methyl transfer enzymes. Active site models of different sizes are used to evaluate the methodology. In particular, the dependence of the calculated energies on the model size, the influence of the dielectric medium, and the particular choice of the dielectric constant are discussed. In addition, we examine the validity of some technical aspects, such as geometry optimization in solvent or with a large basis set, and the use of different density functional methods. PMID:20082388

Georgieva, Polina; Himo, Fahmi

2010-06-01

331

Product-state control of bi-alkali-metal chemical reactions  

SciTech Connect

We consider ultracold, chemically reactive scattering collisions of the diatomic molecules KRb. When two such molecules collide in an ultracold gas, we find that they are energetically forbidden from reacting to form the trimer species K{sub 2}Rb or Rb{sub 2}K, and hence can only react via the bond-swapping reaction 2KRb{yields}K{sub 2}+Rb{sub 2}. Moreover, the tiny energy released in this reaction can in principle be set to zero by applying electric or microwave fields, implying a means of controlling the available reaction channels in a chemical reaction.

Meyer, Edmund R.; Bohn, John L. [JILA, NIST, and University of Colorado, Department of Physics, Boulder, Colorado 80309-0440 (United States)

2010-10-15

332

Product-state control of bi-alkali-metal chemical reactions  

NASA Astrophysics Data System (ADS)

We consider ultracold, chemically reactive scattering collisions of the diatomic molecules KRb. When two such molecules collide in an ultracold gas, we find that they are energetically forbidden from reacting to form the trimer species K2Rb or Rb2K, and hence can only react via the bond-swapping reaction 2KRb?K2+Rb2. Moreover, the tiny energy released in this reaction can in principle be set to zero by applying electric or microwave fields, implying a means of controlling the available reaction channels in a chemical reaction.

Meyer, Edmund R.; Bohn, John L.

2010-10-01

333

Simulation of gas exothermic chemical reaction in porous media reactor with lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

Exothermic reactor is the main part in a chemical heat pump. It involves complex multi-component exothermal chemical reaction in catalyst-filled porous media. The lattice Boltzmann method (LBM) is developed to simulate the characteristics of fluid flow, heat and mass transfer coupling chemical reaction in the exothermic reactor of the isopropanol/acetone/hydrogen chemical heat pump system. Fractal theory is used to structure a porous medium model in the reactor. The simulation results show that LBM is suitable for the simulation and the conversion has an optimal value with different inlet velocities.

Xin, Fang; Li, Xun-Feng; Xu, Min; Huai, Xiu-Lan; Cai, Jun; Guo, Zhi-Xiong

2013-02-01

334

Gas–particle interactions of tropospheric aerosols: Kinetic and thermodynamic perspectives of multiphase chemical reactions, amorphous organic substances, and the activation of cloud condensation nuclei  

Microsoft Academic Search

Aerosols are of central importance in the Earth system, influencing the atmosphere, biosphere, climate, and public health. This article outlines recent advances and perspectives in the investigation and effects of gas–particle interactions in tropospheric aerosols, including physical, chemical and biological aspects. In particular, it addresses how multiphase processes and heterogeneous chemical reactions can be efficiently described by kinetic models, how

Ulrich Pöschl

2011-01-01

335

Chemical and mathematical modeling of asphaltene reaction pathways  

SciTech Connect

Precipitated asphaltene was subjected to pyrolysis and hydropyrolysis, both neat and in solvents, and catalytic hydroprocessing. A solvent extraction procedure defined gas, maltene, asphaltene, and coke product fractions. The apparent first order rate constant for asphaltene conversion at 400/sup 0/C was relatively insensitive to the particular reaction scheme. The yield of gases likewise showed little variation and was always less than 10%. On the other hand, the maltene and coke yields were about 20% and 60%, respectively, from neat pyrolysis, and about 60% and less than 5%, respectively, from catalytic reactions. The temporal variations of the product fractions allowed discernment of asphaltene reaction pathways. The primary reaction of asphaltene was to residual asphaltene, maltenes, and gases. The residual asphaltene reacted thermally to coke and catalytically to maltenes at the expense of coke. Secondary degradation of these primary products led to lighter compounds. Reaction mechanism for pyrolysis of asphaltene model compounds and alkylaromstics were determined. The model compound kinetics results were combined with a stochastic description of asphaltene structure in a mathematical model of asphaltene pyrolysis. Individual molecular product were assigned to either the gas, maltene, asphaltene, or coke product fractions, and summation of the weights of each constituted the model's predictions. The temporal variation of the product fractions from simulated asphaltene pyrolysis compared favorably with experimental results.

Salvage, P.E.

1986-01-01

336

Effect of curvature of the reaction path on dynamic effects in endothermic chemical reactions and product energies in exothermic reactions  

Microsoft Academic Search

Collinear quasiclassical trajectories are examined for two realistic potential energy surfaces for atom?diatomic molecule reactions for two reaction attributes: (1) vibrational energy of the products of a thermal?energy exothermic reaction; (2) threshold energy for endothermic reaction of ground?state reagents. Eight different mass combinations are studied. The potential energy surfaces differ primarily in the amount of potential energy released in an

James W. Duff; Donald G. Truhlar

1975-01-01

337

Chemical reactions and thermal stability of oxygen impurities on graphene  

NASA Astrophysics Data System (ADS)

Oxygen as an impurity is known to degrade conductivity in graphene, but annealing at moderate temperature reverses the effect. Here we report first-principles calculations of oxygen binding and reactions on graphene that elucidate the underlying physics. We find that two O atoms can form an O dimer that can desorb from graphene with an overall activation barrier of 1.3 eV. Oxygen can also be removed in a more complicated reaction in which C atoms in graphene are consumed. We find that structural defects such as Stone-Wales defect and grain boundaries show enhanced binding to O atoms due to the local strain, facilitating the O reaction. If H atoms coexist, an O atom can bind to an H atom forming an OH group, which can also be removed by thermal annealing due to the weak binding, resulting in defect-free graphene.

Wang, Bin; Pantelides, Sokrates

2012-02-01

338

Large-scale prediction of adverse drug reactions using chemical, biological, and phenotypic properties of drugs  

PubMed Central

Objective Adverse drug reaction (ADR) is one of the major causes of failure in drug development. Severe ADRs that go undetected until the post-marketing phase of a drug often lead to patient morbidity. Accurate prediction of potential ADRs is required in the entire life cycle of a drug, including early stages of drug design, different phases of clinical trials, and post-marketing surveillance. Methods Many studies have utilized either chemical structures or molecular pathways of the drugs to predict ADRs. Here, the authors propose a machine-learning-based approach for ADR prediction by integrating the phenotypic characteristics of a drug, including indications and other known ADRs, with the drug's chemical structures and biological properties, including protein targets and pathway information. A large-scale study was conducted to predict 1385 known ADRs of 832 approved drugs, and five machine-learning algorithms for this task were compared. Results This evaluation, based on a fivefold cross-validation, showed that the support vector machine algorithm outperformed the others. Of the three types of information, phenotypic data were the most informative for ADR prediction. When biological and phenotypic features were added to the baseline chemical information, the ADR prediction model achieved significant improvements in area under the curve (from 0.9054 to 0.9524), precision (from 43.37% to 66.17%), and recall (from 49.25% to 63.06%). Most importantly, the proposed model successfully predicted the ADRs associated with withdrawal of rofecoxib and cerivastatin. Conclusion The results suggest that phenotypic information on drugs is valuable for ADR prediction. Moreover, they demonstrate that different models that combine chemical, biological, or phenotypic information can be built from approved drugs, and they have the potential to detect clinically important ADRs in both preclinical and post-marketing phases.

Liu, Mei; Wu, Yonghui; Chen, Yukun; Sun, Jingchun; Zhao, Zhongming; Chen, Xue-wen; Matheny, Michael Edwin

2012-01-01

339

Modeling the Dynamics of Chemical Reactions Involving Multidimensional Tunneling  

NASA Astrophysics Data System (ADS)

The direct dynamics approach is employed to study prototype reactions including hydrogen and hydride transfer. The dynamics are treated with variational transition state theory including multidimensional semiclassical tunneling corrections, and the force field is modeled with semiempirical molecular orbital theory. The primary kinetic isotope effect for the (1,5) sigmatropic rearrangement reaction of cis-1,3-pentadiene is predicted and compared to experiment. The force field is obtained by molecular orbital theory with the AM1, PM3, and MINDO/3 parameterizations. The kinetic isotope effects calculated with the MINDO/3 and PM3 Hamiltonians agree with those calculated by AM1 within 13%, and the latter agree with experiment within 13%. The tunneling contributions to the kinetic isotope effects are analyzed, and the nature of the vibrationally assisted tunneling process is elucidated. The kinetic isotope effects of the reactions of CF_3 with CD_3H are studied including all internal degrees of freedom. The force field necessary for the dynamics calculations is evaluated using the neglect of diatomic differential overlap (NDDO) molecular orbital theory with semiempirical specific -reaction parameters (SRP), which are based on the standard AM1 parameterization adjusted to improve the agreement between experiment and the calculated quantities such as the vibrational frequencies of reactants and products and the classical barrier. The kinetic isotope effects are calculated using two different SRP force fields, and they are in good agreement with the experimental measurements. The picture of the corner cutting tunneling process that emerges is discussed graphically. The two NDDO-SRP models are further used to study the hydrogen abstraction reactions of CF_3 with CH_4, CD_4, and C_2 H_6, and very good agreement with experiment is obtained. Finally, a simple model hydride transfer reaction of formic acid is investigated usine the AM1 and PM3 Hamiltonians, and the results are compared to experiment.

Liu, Yi-Ping

340

Fast growth in phase-separating A-B-copolymer ternary mixtures with a chemical reaction.  

PubMed

We study the dynamics of phase separation of a binary A-B- polymer mixture with copolymer C, which is produced by the reaction of two counterpart reactive polymers A and B at the interface via the chemical reaction A+B right harpoon over left harpoon C. For low interfacial energy between the A and B phases, where the copolymer prefers to locate at interfaces, we show that the chemical reaction accelerates the phase separation of the system dramatically, because the backward reaction always drives the creation of immiscible A and B pairs at interfaces, which speed up the phase separation of the system, while the forward reaction process becomes more and more difficult as the interfaces are gradually saturated by copolymers. We also indicate that for a fixed chemical reaction rate constant, as the initial concentration of the copolymers increases, the domain growth at the late stage is speeded up as a result of the backward chemical reaction. However, when the interfacial energy is high, both forward and backward reactions coexist due to the occurrence of unsaturated interfaces, but the relative strength of reaction rates has no appreciable effect on domain growth during spinodal decomposition, because the interfacial energy dominates phase separation. PMID:12636705

Zhu, Yue-Jin; Ma, Yu-Qiang

2003-02-14

341

Chemical analyses of geothermal waters and Strategic Petroleum Reserve brines for metals of economic importance  

Microsoft Academic Search

Waters from seven hydrothermal-geothermal, one geopressured-geothermal, and six Strategic Petroleum Reserve wells have been surveyed for 12 metals of economic importance using trace chemical analysis techniques. The elements sought were Cr, Co, Mn, Ta, Sn, V, Nb, Li, Sr, Pt, Au and Ag. Platinum was found at a concentration of approx. 50 ppb in a brine from the Salton Sea

J. E. Harrar; E. Raber

1984-01-01

342

Organoberyllium compounds and their chemical reactions. XI. Synthesis of diacetylhydrobenzoins  

SciTech Connect

The authors previously determined that the reaction of aromatic aldehydes with acylhaloberyllium in ethyl acetate lead to the formation of stilbene. In this same vein they have found that the final products of this reaction can include not only stilbenes but also diacetylhydrobenzoin and that the product is determined by the nature of the solvent. In this paper they determine that while ethyl acetate indeed leads to the stilbene the use of an ether--diethyl or diisopropyl--leads to diacetylhydrobenzoin. NMR spectroscopy is used to ascertain the structure of the product.

Lapkin, I.I.; Sinani, S.V.

1987-08-10

343

The Bergman reaction of dynemicin A a quantum chemical investigation  

NASA Astrophysics Data System (ADS)

For the first time, the Bergman reaction of a naturally occurring enediyne, namely dynemicin A, is fully investigated at the DFT level of theory using the B3LYP hybrid functional and VDZ basis sets. The calculated geometry of dynemicin A agrees well with the X-ray structure of deoxydynemicin A. The activation barrier is calculated to be 19.4 kcal/mol, while the reaction energy is exothermic by -2.1 kcal/mol, reflecting the destabilization of the enediyne unit by incorporation into a tricyclic ring system. The energetics of dynemicin A reveal that the enediyne is biologically active at body temperature.

Ahlström, Bodil; Kraka, Elfi; Cremer, Dieter

2002-07-01

344

Asymptotic behaviour of a general reversible chemical reaction-diffusion equation  

Microsoft Academic Search

In this work, we prove the existence and the exponential decay to equilibrium of a general reversible chemical reaction-diffusion equation with same but general diffusion. Moreover, we prove the optimal asymptotic behaviour in the \\

Ivan Gentil; Boguslaw Zegarlinski

2009-01-01

345

Spectroscopic Studies of Chemical Adsorption and Reactions at Transition Metal Surfaces.  

National Technical Information Service (NTIS)

The accomplishments of the work under the title 'Spectroscopic Studies of Chemical Adsorption and Reactions at Transition Metal Surfaces' are summarized. Included are studies of flat and stepped surfaces, of surfaces with chemisorbed species and of reacti...

J. E. Demuth G. W. Rubloff

1977-01-01

346

Numerical simulations of heterogeneous chemical reactions coupled to fluid flow in varying thermal fields.  

National Technical Information Service (NTIS)

A numerical simulator of reactive chemical transport with coupling from precipitation-dissolution reactions to fluid flow, via changes of porosity and permeability, is applied to precipitation-dissolution of quartz and calcite in spatially and temporally ...

C. L. Carnahan

1991-01-01

347

Detailed Chemical Kinetic Reaction Mechanism for Oxidation of Four Small Alkyl Esters in Laminar Premixed Flames.  

National Technical Information Service (NTIS)

A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate and ethyl acetate. This mechanism is validated by comparisons between computed resul...

C. K. Westbrook F. L. Dryer M. Chaos P. R. Westmoreland W. J. Pitz

2008-01-01

348

EVALUATION OF CHEMICAL REACTION MECHANISMS FOR PHOTOCHEMICAL SMOG. PART 2. QUANTITATIVE EVALUATION OF THE MECHANISMS (REVISED)  

EPA Science Inventory

Six chemical reaction mechanisms for photochemical smog were analyzed to determine why, under identical conditions, they predict different maximum ozone concentrations. To perform the analysis, a counter species technique was used to determine the contributions of individual reac...

349

Detailed chemical kinetic reaction mechanism for oxidation of n-octane and iso-octane  

SciTech Connect

The development of detailed chemical kinetic reaction mechanisms for oxidation of n-octane and iso-octane is described, with emphasis on the factors which are specific to many large hydrocarbon fuel molecules. Elements which are of particular importance are found to include site-specific abstraction of H atoms, radical isomerization of alkyl radicals by internal H atom abstraction, and rapid ..beta..-scission of the alkyl radicals. These features, combined with distinctions in the types of intermediate olefin species produced, are used to explain the significant differences in the rate of oxidation between n-octane and iso-octane. Experimental results from the turbulent flow reactor and low pressure laminar flames, using both n-octane and iso-octane as fuels, are used to test the reaction mechanisms and indicate those parts of the total mechanisms which are in greatest need of further development and refinement. It is found that the submechanisms for consumption of the C/sub 2/ - C/sub 4/ olefins need further attention, particularly the identification of the major product species distributions and their temperature dependence for reactions of these olefins and radicals including O and OH. 24 refs., 3 figs., 4 tabs.

Axelsson, E.I.; Brezinsky, K.; Dryer, F.L.; Pitz, W.J.; Westbrook, C.K.

1986-04-15

350

New measurements for the astrophysically important calcium-40(alpha,gamma)titanium-44 reaction  

NASA Astrophysics Data System (ADS)

The 40Ca(alpha,gamma)44Ti reaction is thought to be the main production method for the short-lived radionuclide, 44Ti (t1/2 = 58.9 +/- 0.3 yr). Production in the alpha-rich freeze-out zone of a core-collapse supernova makes 44Ti an important nuclide in the understanding of nucleosynthesis in explosive stellar environments. A new measurement of the 40Ca(alpha,gamma) 44Ti reaction has been performed through two different experimental approaches. During this work, a new accelerator mass spectrometry (AMS) facility was developed and commissioned at the University of Notre Dame, primarily for the measurement of reaction cross-sections of astrophysical interest. Using this facility, a series of 44Ti activation measurements were performed with a 40Ca beam incident on a 4He gas target. The four discrete energy ranges over which the activations occurred all lie within the temperature range relevant for alpha-rich freeze-out. Further to this, an excitation curve was measured over the energy range E alpha = 4600 - 3000 keV, using alpha-particles incident on a 40Ca target. The good agreement between these two results resulted in the successful commissioning of the AMS facility. The new reaction rates derived in this work results in an increased expected yield of 44Ti in proposed supernova environments (for example Cassiopeia A) by ˜ 40 %, when compared to 1D supernova models using reaction rates based on previous prompt gamma-ray studies .

Robertson, Daniel J.

351

Signatures of chemical reactions in the morphology and fluctuations of giant vesicles  

NASA Astrophysics Data System (ADS)

The behaviour of an amphiphilic membrane is determined by the physical and chemical properties of the molecules which form the bilayer and their interactions with the surrounding medium. Bulk or interfacial chemical reactions modify interaction parameters and/or affect directly the chemical composition of the membrane. We monitor the morphological response and the thermal fluctuations of giant lipid vesicles to chemical reactions in the external vesicle medium using phase-contrast microscopy. Observation of vesicle conformations as a function of time allows us to characterize the statics and dynamics of membrane response as well as the underlying chemical kinetics. As two examples, we present (a) a photochemical reaction of hexacyanoferrate which induces an increase in pH and (b) the enzymatic cleavage of phosphatidyl choline by the phospholipase C from Bacillus cereus.

Döbereiner, Hans-Günther; Petrov, Peter G.; Riske, Karin A.

2003-01-01

352

Exothermic and endothermic chemical reactions involving very many particles modeled with molecular dynamics  

Microsoft Academic Search

The traditional continuum approach of modeling chemical reactions with specified kinetic rates suffers from numerical difficulties in reactive flows and other highly non-equilibrium situations due to the stiffness of the differential equations in both space and time. These drawbacks can be eliminated within the framework of the discrete-particle approach in which the chemical reactions are modeled by means of two-body

Witold Alda; David A. Yuen; Hans-Peter Lüthi; James R. Rustad

2000-01-01

353

[From a periodic chemical reaction to the dynamics of microbial communities].  

PubMed

The first articles published by Anatol Zhabotinsky have been analyzed. The mechanisms of the Belousov-Zhabotinsky and Bray-Liebhafsky oscillating chemical reactions were compared. It was shown that the traditional chemical kinetics, the new methods of molecular biology as well as isotopic composition analysis made it possible to consider new constraints concerning the degradation of organic matter and microbial dynamics. A mathematical model was developed to describe isotope accumulation in biomass and reaction products. PMID:20067197

Vavilin, V A

354

Determination of Activation Energies of Chemical Reactions by Differential Thermal Analysis  

Microsoft Academic Search

A NUMBER of articles have been published dealing with the differential thermal analysis (DTA) of chemical reaction kinetics1-5. Only one of these, however, gives a direct method for determining the activation energy (E) of the chemical reaction4. In this method, DTA curves are recorded at several different rates of heating. The results are then plotted as ln b\\/Tm2 against 1\\/Tm,

G. O. Piloyan; I. D. Ryabchikov; O. S. Novikova

1966-01-01

355

From simple to complex and backwards. Chemical reactions under very high pressure  

NASA Astrophysics Data System (ADS)

High pressure chemical reactions of molecular systems are discussed considering the various factors that can affect the reactivity. These include steric hindrance and geometrical constraints in the confined environment of crystals at high pressure, changes of the free energy landscape with pressure, photoactivation by two-photon absorption, local and collective effects. A classification of the chemical reactions at high pressure is attempted on the basis of the prevailing factors.

Bini, Roberto; Ceppatelli, Matteo; Citroni, Margherita; Schettino, Vincenzo

2012-04-01

356

Quantum chemical study of aluminum CVD reaction for titanium nitride (111) surface with terminal fluorine  

Microsoft Academic Search

Reaction mechanisms and interface structures in aluminum (Al) chemical vapor deposition (CVD) have been investigated in terms of the surface termination models for TiN by ab initio quantum chemical approach. The B3LYP density functional calculations and coupled-cluster calculations were carried out by using the local structural models in order to investigate reaction mechanisms, and we found Al can be deposited

A. Tachibana; K. Nakamura

2000-01-01

357

Microfluidic sub-millisecond mixers for the study of chemical reaction kinetics  

Microsoft Academic Search

We present a micromachined, high Reynolds number (2000-6000), sub-millisecond liquid mixer for the study of chemical reaction kinetics. This 1 cm×1 cm×1 mm bulk micromachined silicon mixer is capable of initiating and quenching (starting and stopping) chemical reactions in intervals as short as 100 ?s. The centimeter sized mixer chip contains two tee mixers connected by one channel which serves

Amish Desai; D. Bokenkamp; Xing Yang; Yu-Chong Tai; E. Marzluff; S. Mayo

1997-01-01

358

Studies on the Role of Radiation in Chemical Reactions Occurring on Surfaces  

Microsoft Academic Search

The addition of energetic radiation to a gas-solid surface system may initiate or enhance chemical reactions occurring on the surface. Conversely, when a chemical reaction proceeds on a surface, radiation may be spontaneously emitted. The effect of argon ion bombardment on SiO(,2) exposed to XeF(,2) was studied. At room temperature SiO(,2) adsorbs a monolayer of fluorine when exposed to XeF(,2).

Michael Allen Loudiana

1984-01-01

359

Thermal Analysis of Chemical Reaction Process Forming CuInSe 2 Crystal  

Microsoft Academic Search

In order to establish the preparation method of high-quality CuInSe2 single crystals, we have investigated the chemical reaction process of CuInSe2 by differential thermal analysis and by powder X-ray diffraction measurements. It is confirmed that CuInSe2 compound undergoes a phase transition from chalcopyrite to sphalerite structure at 815°C and melts at 996°C. In the chemical reaction process of a Cu+In+2Se

Hiroaki Matsushita; Takeo Takizawa

1995-01-01

360

EC mechanism of an adsorbed redox couple. Volume vs surface chemical reaction  

Microsoft Academic Search

A theoretical model of a complex electrode mechanism coupled by adsorption of the redox couple and followed by two different types of irreversible chemical reactions is developed:Ox(ads)+ne??Red(ads)?ksP??(Ox(aq))x=0+ne??(Red(aq))x=0?kvPThe theoretical consideration for this specific type of EC mechanism comprises all relevant phenomena such as diffusion mass transport, adsorption equilibria and kinetics of the following irreversible chemical reactions. The adsorbed electroactive product Red(ads)

Valentin Mir?eski; Milivoj Lovri?

2004-01-01

361

Chemical reactions in the low-temperature zone of a laminar rich propane—air flame  

Microsoft Academic Search

The mechanism of chemical reactions in the low-temperature zone of a rich propane—air flame is considered. It is shown that\\u000a at temperatures of 300–700 K, intense chemical reactions proceed with the formation of end products and that the water concentration\\u000a reaches an intermediate equilibrium value even at a temperature of 685 K. In this zone of the front, the diffusion

V. A. Bunev; V. S. Babkin

2006-01-01

362

Chemical Principles Revisited. Redox Reactions and the Electropotential Axis.  

ERIC Educational Resources Information Center

This paper suggests a nontraditional pedagogic approach to the subject of redox reactions and electrode potentials suitable for freshman chemistry. Presented is a method for the representation of galvanic cells without the introduction of the symbology and notation of conventional cell diagrams. (CW)

Vella, Alfred J.

1990-01-01

363

Effects of Chemical Reactions on the Bimolecular Rate Constant  

Microsoft Academic Search

The dependence of the bimolecular rate constant on the reaction rate, degree of anisotropic scattering, mass ratio, and other parameters is investigated by considering the Boltzmann equation for a dilute homogeneous reacting gas. For highly anisotropic elastic scattering, a differential form of the Boltzmann equation is derived and a solution obtained, which yields an analytical expression for the rate constant.

M. D. Kostin

1967-01-01

364

The Quantum Mechanics of Chemical Reactions Involving Conjugate Double Bonds  

Microsoft Academic Search

The various theories of conjugate double bonds are discussed on the basis of quantum mechanics. The potential energy surfaces for the addition of diatomic molecules to such bonds are calculated by the generalized Heitler-London method. It is shown that various mechanisms are possible for such reactions and that such effects as the steric repulsions of the various inactive groups in

Henry Eyring; Albert Sherman; George E. Kimball

1933-01-01

365

Acoustic wave propagation in fluids with coupled chemical reactions  

Microsoft Academic Search

This investigation presents a hydroacoustic theory which accounts for sound absorption and dispersion in a multicomponent mixture of reacting fluids (assuming a set of first-order acoustic equations without diffusion) such that several coupled reactions can occur simultaneously. General results are obtained in the form of a biquadratic characteristic equation (called the Kirchhoff-Langevin equation) for the complex propagation variable chi =

T. S. Margulies; W. H. Schwarz

1984-01-01

366

Ozonolysis of Mixed Oleic-Acid/Stearic-Acid Particles: Reaction Kinetics and Chemical Morphology  

NASA Astrophysics Data System (ADS)

Atmospheric particles directly and indirectly affect global climate and have a primary role in regional issues of air pollution, visibility, and human health. Atmospheric particles have a variety of shapes, dimensions, and chemical compositions, and these physicochemical properties evolve (i.e., "age") during transport of the particles through the atmosphere, in part because of the chemical reactions of particle-phase organic molecules with gas-phase atmospheric oxidants. As a global average, hydroxyl radical (OH) and ozone (O3) are responsible quantitatively for most oxidant aging of atmospheric particles. The reactions of the hydroxyl radical occur in the surface region of a particle because of the nearly diffusion-limited bimolecular rate constant of OH with a variety of organic molecules. Ozone, on the other hand, is a selective agent for the unsaturated bonds of organic molecules and may diffuse a considerable distance into particles prior to reaction. The reaction of oleic acid with ozone has recently emerged as a model system to better understand the atmospheric chemical oxidation processes affecting organic particles. The ozonolysis of mixed oleic-acid/stearic-acid (OL/SA) aerosol particles from 0/100 to 100/0 weight percent composition is studied. The magnitude of the divergence of the particle beam inside an aerosol mass spectrometer shows that, in the concentration range 100/0 to 60/40, the mixed OL/SA particles are liquid prior to reaction. Upon ozonolysis, particles with SA composition greater than 25% change shape, indicating that they have solidified. Transmission electron micrographs show that SA(s) forms needles. For SA compositions greater than 10%, the reaction kinetics exhibit an initial fast decay of OL for low O3 exposure with no further loss of OL at higher O3 exposures. For compositions from 50/50 to 10/90, the residual OL concentration remains at 28+/-2% of its initial value. The initial reactive uptake coefficient for O3, as determined by OL loss, decreases linearly from 1.25(+/-0.2) 10-3 to 0.60(+/-0.15) 10-3 for composition changes of 100/0 to 60/40. At 50/50 composition, the uptake coefficient drops abruptly to 0.15(+/-0.1) 10-3, and there are no further changes with increased SA content. The amount of SA in the particles also decreases during OL ozonolysis. The stabilized Criegee intermediate (SCI) formed by OL ozonolysis attacks the carboxylic acid group of SA to yield an acyloxyalkyl hydroperoxide product. The experimental observations of this study can be explained by the following two postulates: (1) unreacted mixed particles remain as supersatured liquids up to 60/40 composition and (2) SA, as it solidifies, locks in a significant amount of oleic acid. The results of this study point out the important effects of particle phase, composition, and morphology on chemical reactivity. Oleic acid in liquid regions of a particle reacts rapidly with O3 whereas OL trapped inside solid SA is essentially unavailable for reaction with O3. These results contribute to the continuing development of the scientific community's understanding of particle aging process in the atmosphere, for which the ultimate goal is to provide quantitative mechanistic models of physicochemical transformations under atmospheric conditions.

Martin, S. T.; Katrib, Y.; Biskos, G.; Buseck, P. R.; Davidovits, P.; Jayne, J. T.; Mochida, M.; Wise, M. E.; Worsnop, D. R.

2005-12-01

367

Spontaneous Motion of a Droplet Coupled with Chemical Reaction  

Microsoft Academic Search

The spontaneous motion of a droplet of Belousov-Zhabotinsky (BZ) reactionmedium was studied experimentally. A propagating chemical wave causes an increase in interfacial tension, which induces convection inside the droplet. This convection causes spontaneous translational motion of the droplet. In this article, we describe the dynamics of the convection inside the droplet and discuss its mechanism.

Hiroyuki Kitahata

2006-01-01

368

Single-molecule chemical reactions on DNA origami  

Microsoft Academic Search

DNA nanotechnology and particularly DNA origami, in which long, single-stranded DNA molecules are folded into predetermined shapes, can be used to form complex self-assembled nanostructures. Although DNA itself has limited chemical, optical or electronic functionality, DNA nanostructures can serve as templates for building materials with new functional properties. Relatively large nanocomponents such as nanoparticles and biomolecules can also be integrated

Niels V. Voigt; Thomas Tørring; Alexandru Rotaru; Mikkel F. Jacobsen; Jens B. Ravnsbæk; Ramesh Subramani; Wael Mamdouh; Jørgen Kjems; Andriy Mokhir; Flemming Besenbacher; Kurt Vesterager Gothelf

2010-01-01

369

Observation of a chemical reaction using a micromechanical sensor  

Microsoft Academic Search

We describe a new form of calorimeter designed for use in gaseous and vacuum environments which can sense chemical reac- tions with an estimated sensitivity limit of % 1 pJ. The device is based on a micromechanical Si lever coated with a thick layer of Al upon which a sample in the form of a thin layer is fixed or

J. K. Gimzewski; Ch. Gerber; E. Meyer; R. R. Schlittler

1994-01-01

370

Control and detection of chemical reactions in microfluidic systems  

Microsoft Academic Search

Recent years have seen considerable progress in the development of microfabricated systems for use in the chemical and biological sciences. Much development has been driven by a need to perform rapid measurements on small sample volumes. However, at a more primary level, interest in miniaturized analytical systems has been stimulated by the fact that physical processes can be more easily

Andrew J. deMello

2006-01-01

371

Chemical-biological reactions common to teratogenesis and mutagenesis  

PubMed Central

Cytotoxic chemicals have in common the ability to act specifically on cells in cycle. Bacteria are more sensitive in the exponential growth phase than when growing slowly in media. Similar observations have been made on a variety of systems ranging from bacteria, yeast, higher plants and invertebrates to vertebrates including primates. The embryo and fetus are highly susceptible to cytotoxic agents because they have continuous groups of cells in the growth phase. Acutely toxic doses may cause cellular death and result in developmental defects or fetal death. Cytotoxic agents can be grouped as alkylating agents, electrophilic reactants, antimetabolites, intercalating agents, amino acid antagonists, spindle poisons, and an additional group of chemicals which covalently bind to DNA. These cytotoxic groups of chemicals may also be mutagenic by interacting with DNA to produce changes in sequences of nucleotides resulting in heritable defects either in a somatic cell line or in a germinal cell line. The mechanisms of chemical-induced teratogenicity and mutagenicity are similar. This commonality is further discussed in the text.

Harbison, Raymond D.

1978-01-01

372

Chemical Reactions and Cloud Nucleation on Soot Aerosols  

Microsoft Academic Search

Incomplete combustion causes enhanced levels of soot aerosols and polycyclic aromatic hydrocarbons in the urban atmosphere. In turn, the increased abundance of aerosols may facilitate increased cloudiness by acting as cloud condensation nuclei (CCN) and ice nuclei (IN). The goal of our study is to first identify and quantify chemical changes in atmospheric aerosols, such as the formation of surface

S. D. Brooks; L. Mason; A. Fornea

2006-01-01

373

X-ray Microspectroscopy and Chemical Reactions in Soil Microsites  

Microsoft Academic Search

Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context

D Hesterberg; M Duff; J Dixon; M Vepraskas

2011-01-01

374

EFFICIENT CHEMICAL TRANSFORMATIONS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The diverse nature of chemical entities requires various green' strategic pathways in our quest towards attaining sustainability. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable...

375

Chemical reaction induced agglomeration and defluidization of fluidized beds  

Microsoft Academic Search

Industrial fluidized beds are operated with particles that usually contain impurities or are themselves a mixture of many components (for example, ores). Upon heating to high temperatures, some of these components soften, melt or react with each other, generating stickiness. In fluid bed reactors, the fluidizing gas can also react chemically with the solids producing new components and during this

Gabriel Tardos; Robert Pfeffer

1995-01-01

376

Chemical Reactions and Cloud Nucleation on Soot Aerosols  

NASA Astrophysics Data System (ADS)

Incomplete combustion causes enhanced levels of soot aerosols and polycyclic aromatic hydrocarbons in the urban atmosphere. In turn, the increased abundance of aerosols may facilitate increased cloudiness by acting as cloud condensation nuclei (CCN) and ice nuclei (IN). The goal of our study is to first identify and quantify chemical changes in atmospheric aerosols, such as the formation of surface hydrophilic functional groups upon exposed to ozone, and second, to assess the cloud nucleating ability of the oxidized aerosols. When first introduced into the atmosphere, soot is a hydrophobic substance and relatively poor CCN or IN. As soot encounters atmospheric oxidizing agents, such as ozone, its surface chemical properties may be altered. Thus, the soot particles become hydrophilic, and subsequently may be much more efficient cloud nuclei. In this study, soot samples are generated using various fuel sources including diesel and propane. Using a Fourier Transform Infrared Spectrometer equipped with a Horizontal Attenuated Total Reflectance cell, we observe the chemical changes at the soot surface as a function of ozone exposure. In addition, the ice nucleating ability of fresh and chemically aged soot is identified using a microscope cooling apparatus. Results will be presented and atmospheric implications discussed.

Brooks, S. D.; Mason, L.; Fornea, A.

2006-12-01

377

Localized open systems in a thermodynamically closed system of chemical reactions  

Microsoft Academic Search

A thermodynamically closed system of chemical reactions becomes unstable against transforming spontaneously a locally planar reaction network into a spherically shaped one if the mean lifetime of the composite two-monomers is greater than the mean collision time of the polymers.

Koichiro Matsuno

1979-01-01

378

Intracellular click reaction with a fluorescent chemical Ca2+ indicator to prolong its cytosolic retention.  

PubMed

The powerful strategy of "intracellular click reaction" was used to retain a chemical Ca(2+) indicator in the cytosol. Specifically, a novel clickable Ca(2+) indicator "N3-fura-2 AM" was coupled with dibenzylcyclooctyl-modified biomacromolecules via copper-free click reaction in living cells and Ca(2+) oscillation was observed for an extended period of time. PMID:23851490

Takei, Yoshiaki; Murata, Atsushi; Yamagishi, Kento; Arai, Satoshi; Nakamura, Hideki; Inoue, Takafumi; Takeoka, Shinji

2013-08-25

379

Developing a New Air Pollution Dispersion Model with Chemical Reactions Based on Multiple Cell Approach  

Microsoft Academic Search

A two dimensional atmospheric dispersion model for computation of the ambient air concentration of reactive pollutants emitted from ground level sources is described. Atmospheric chemical reactions are the most complicated and stiff part of pollutants dispersion equations. Coupling them with other physical transport processes to assemble an integrated dispersion model is a time consuming and complicated matter. Mechanism of reactions

Ali Alizadeh Osalu; Mohammad Ali Kaynejad; Esmaeil Fatehifar; ALI ELKAMEL

2009-01-01

380

Progression in high school students (aged 16-18) conceptualizations about chemical reactions in solution  

Microsoft Academic Search

The purpose of this study was to explore the development over time of students' understandings of the concept of chemical reaction in the context of two familiar reactions in solution. The study is based on interviews of 48 students, aged 16-18, who had been successful in their year 11 examinations and had selected to study chemistry as one of their

Hong-Kwen Boo; J. R. Watson

2001-01-01

381

MODELING OF GAS ABSORPTION ACCOMPANIED BY CHEMICAL REACTION IN DOWNFLOW CO-CURRENT PACKED COLUMNS  

Microsoft Academic Search

A mathematical model is presented for gas absorption accompanied by chemical reaction in downflow cocurrent packed columns. The model incorporates an axial dispersed plug flow for the bulk gas and dynamic liquid phases and a Fickian type equation for the stagnant liquid phase. The reaction is considered to be occurring in both the dynamic and stagnant liquid phases. Numerical simulations

S. A. BEG; M. M. HASSAN; M. S. M. NAQVI

1998-01-01

382

A Tunable Chemical Pattern Filter Constructed by Networks of Reaction Compartments and Tubes  

Microsoft Academic Search

We study numerically the filtering capabilities of nanoscale networks built up of containers and tubes hosting chemical reactions. Spatio-temporal patterns of substrate molecules are injected into the network. The substrate propagates by diffusion and reacts with enzymes distributed in the network prior to the injections. The dimensions of the network are tailored in a way that the transport and reaction

Ludvig Lizana; Zoran Konkoli; Owe Orwar

2007-01-01

383

The Quantum Mechanics of Chemical Kinetics of Homogeneous Gas Phase Reactions I. General Considerations  

Microsoft Academic Search

From the zeroth order Born-Oppenheimer approximation to the wave functions of a molecular system and the first order time-dependent perturbation theory of quantum mechanics it has been possible to deduce: (1) the adiabatic hypothesis; (2) the dependence of the rate of homogeneous gas phase chemical reactions upon the composition of reaction mixtures; (3) the condition for zero net rate of

Sidney Golden

1949-01-01

384

Bimolecular gas-phase reactions in the Kramers theory of chemical kinetics @fa@f)  

Microsoft Academic Search

An expression for the rate constant is obtained for a bimolecular gas?phase reaction via an extended version of the Kramers theory of chemical kinetics. The multicomponent Fokker–Planck equation is transformed into a suitable set of relative coordinates that facilitated the derivation. The derived expression for the rate constant shows explicitly how the rate of reaction depends on the potential energy

R. S. Larson; M. D. Kostin

1984-01-01

385

Influence of mineral weathering reactions on the chemical composition of soil water, springs, and ground water, Catoctin Mountains, Maryland  

USGS Publications Warehouse

During 1983 and 1984, wet precipitation was primarily a solution of dilute sulphuric acid, whereas calcium and bicarbonate were the major ions in springs and ground water in two small watersheds with a deciduous forest cover in central Maryland. Dominant ions in soil water were calcium, magnesium, and sulphate. The relative importance of mineral weathering reactions on the chemical composition of these subsurface waters was compared to the contribution from wet precipitation, biological processes, and road deicing salts. -from Author

Katz, B. G.

1989-01-01

386

Effect of Coriolis coupling in chemical reaction dynamics.  

PubMed

It is essential to evaluate the role of Coriolis coupling effect in molecular reaction dynamics. Here we consider Coriolis coupling effect in quantum reactive scattering calculations in the context of both adiabaticity and nonadiabaticity, with particular emphasis on examining the role of Coriolis coupling effect in reaction dynamics of triatomic molecular systems. We present the results of our own calculations by the time-dependent quantum wave packet approach for H + D2 and F(2P3/2,2P1/2) + H2 as well as for the ion-molecule collisions of He + H2 +, D(-) + H2, H(-) + D2, and D+ + H2, after reviewing in detail other related research efforts on this issue. PMID:18446243

Chu, Tian-Shu; Han, Ke-Li

2008-03-05

387

Efficiency of a stirred chemical reaction in a closed vessel  

NASA Astrophysics Data System (ADS)

We perform a numerical study of the burning efficiency in a closed vessel. Starting with a little spot of product, we compute the time needed to complete the reaction in the container. Inside the vessel there is a cellular flow that transports the reactants. Our main result is that if the size of the container is not very large compared with the typical length of the velocity field, one has a plateau of the burning time as a function of the strength of the velocity field, U. This means that, once the plateau is reached, a further increase of U does not reduce the time needed to complete the reaction. This plateau arises when we consider both a stationary and a time-dependent cellular flow, and we give analytical and numerical arguments that try to explain why it appears. Also a comparison of the results for the finite system with the infinite case shows the dramatic effect of the finite size.

López, C.; Vergni, D.; Vulpiani, A.

2002-09-01

388

The numerical simulation of viscous flows with change of phase and chemical reaction  

Microsoft Academic Search

A computational procedure, based on the finite element method, is developed to study the fluid dynamics of a chemically reacting system. Specifically, the problem involves the phase change (gelation) of an incompressible liquid due to an exothermic chemical reaction. Typical thermosetting materials are considered under conditions of both buoyancy-driven and forced flow. The focus of the present article is on

D. K. Gartling

1988-01-01

389

Equations of motion of a gas mixture in the presence of chemical reactions  

Microsoft Academic Search

Equations of multicomponent, multivelocioty gasdynamics taking physical and chemical transformations into account are obtained for a multicomponent gas mixture with a small addition of charged particles in a strong electric field. The charged particles serve to excite specific internal energy states of the neutral molecules, and chemical reactions occur between the neutral molecules. It is shown that, when there are

V. Iu. Velikodnyi

1990-01-01

390

Industrial pyrolysis of cellulosic materials. [Chemical reactions occurring during pyrolysis and analysis of volatile fractions  

Microsoft Academic Search

Industrial pyrolysis of cellulosic materials to various fuels and chemicals requires an understanding of the complex reactions involved and how they can be controlled to provide acceptable yields. Investigation of a variety of model compounds and cellulosic substrates by modern methods of thermal and chemical analysis has shown that initial pyrolysis of glycosidically linked compounds takes place through transglycosylation to

Shafizadeh

1975-01-01

391

Chemical bonding and reactions at the Pd\\/Si interface  

Microsoft Academic Search

The electronic structure of the clean Pd\\/Si(111) and Pd\\/Si(100) interfaces has been investigated using angle-integrated and angle-resolved ultraviolet photoemission (UPS) and Auger electron spectroscopies (AES), in conjunction with transmission electron microscopy (TEM), work-function, and low-energy electron diffraction measurements. Since the interface is highly reactive, studies were made by processing the reaction in two ways: (i) sequential annealing steps of thick

G. W. Rubloff; P. S. Ho; J. F. Freeouf; J. E. Lewis

1981-01-01

392

Efficiency of a stirred chemical reaction in a closed vessel  

Microsoft Academic Search

:   We perform a numerical study of the burning efficiency in a closed vessel. Starting with a little spot of product, we compute\\u000a the time needed to complete the reaction in the container. Inside the vessel there is a cellular flow that transports the\\u000a reactants. Our main result is that if the size of the container is not very large

C. López; Davide Vergni; Angelo Vulpiani

2002-01-01

393

FTIR in situ studies of the gas phase reactions in chemical vapor deposition of SiC  

SciTech Connect

The gas phase during the chemical vapor deposition of silicon carbide from CH{sub 3}SiCl{sub 3} has been investigated by means of FTIR spectroscopy in the in situ conditions. Results show the formation of SiCl{sub 4} and CH{sub 4} molecules which are the transition products in the deposition process, according to earlier suppositions. The gas phase reaction induced by small amounts of HCl (or H{sub 2}O) in the system is an autocatalytic one. The mechanism of surface reactions is proposed. The importance of gas phase analysis in the deposition process is indicated.

Jonas, S.; Ptak, W.S.; Sadowski, W.; Walasek, E. [Univ. of Mining and Metallurgy, Krakow (Poland). Dept. of Ceramics; Paluszkiewicz, C. [Jagiellonian Univ., Krakow (Poland). Regional Lab.

1995-07-01

394

Chemical reactions between cold trapped Ba+ ions and neutral molecules in the gas phase  

Microsoft Academic Search

Using a laser-cooled ion trapping apparatus, we have investigated laser-induced chemical reactions between cold trapped Ba+ ions and several neutral molecular gases at room temperature, O2 , CO2 , and N2O , leading to the production of cold trapped (≈20mK) BaO+ ions. The BaO+ ions were converted back to Ba+ ions via reaction with room-temperature CO. Reaction rates were determined

B. Roth; D. Offenberg; C. B. Zhang; S. Schiller

2008-01-01

395

Ion-Molecule Reactions and Chemical Composition of Emanated from Herculane Spa Geothermal Sources  

PubMed Central

The paper presents a chemical composition analysis of the gases emanated from geothermal sources in the Herculane Spa area (Romania). The upper homologues of methane have been identified in these gases. An ion-molecule reaction mechanism could be implicated in the formation of the upper homologues of methane. The CH4+ ions that appear under the action of radiation are the starting point of these reactions. The presence of hydrogen in the emanated gases may be also a result of these reactions.

Cosma, Constantin; Suciu, Ioan; Jantschi, Lorentz; Bolboaca, Sorana D.

2008-01-01

396

Gas-phase chemical reactions of transition metal clusters with simple molecules  

Microsoft Academic Search

Chemical reactions of isolated transition metal clusters are studied in a laser-vaporization cluster source coupled to a continuous-flow reactor. Detection of reaction products is via laser ionization and time-of-flight mass spectrometry. Experimental probes that have been developed include: (1) kinetics measurements, in which the disappearance of bare cluster signal with increasing reagent gas flow is used to determine absolute reaction

S. J. Riley; E. K. Parks

1986-01-01

397

Chemical reactions for a deuteration network (Vastel+, 2012)  

NASA Astrophysics Data System (ADS)

The ground-state rotational ortho-D2H+(1,1,1-0,0,0) transition at 1476.6GHz in the prestellar core 16293E has been searched for with the Herschel/HIFI instrument, within the CHESS (Chemical HErschel Surveys of Star forming regions) Key Program. The line has not been detected at the 21mK.km/s level (3 sigma integrated line intensity). We used the ortho-H2D+ 110-111 transition and para-D2H+ 110-101 transition detected in this source to determine an upper limit on the ortho-to-para D2H+ ratio as well as the para-D2H+/ortho-H2D+ ratio from a non-LTE analysis. We then compared our chemical modeling with the observations in order to estimate the CO depletion as well as the H2 density and kinetic temperature at the position observed. The chemical network is provided in the kida.dat file. (1 data file).

Vastel, C.; Caselli, P.; Ceccarelli, C.; Bacmann, A.; Lis, D. C.; Caux, E.; Codella, C.; Beckwith, J. A.; Ridley, T.

2012-09-01

398

A Decoupling Procedure for Simulating Fluid Mixing, Heat Transfer and Non-Equilibrium Redox Chemical Reactions in Fluid-Saturated Porous Rocks  

Microsoft Academic Search

Non-equilibrium redox chemical reactions of high orders are ubiquitous in fluid-saturated porous rocks within the crust of\\u000a the Earth. They play a very important role in ore body formation and alteration closely associated with a mineralizing system.\\u000a Since pore-fluid is a major carrier transporting chemical species from one part of the crust into another, the chemical process\\u000a is coupled with

Chongbin Zhao; Bruce Hobbs; Alison Ord

399

Travelling waves of auto-catalytic chemical reaction of general order—An elliptic approach  

Microsoft Academic Search

In this paper we study the existence and non-existence of travelling wave to parabolic system of the form at=axx?af(b), bt=Dbxx+af(b), with f a degenerate nonlinearity. In the context of an auto-catalytic chemical reaction, a is the density of a chemical species called reactant A, b that of another chemical species B called auto-catalyst, and D=DB\\/DA>0 is the ratio of diffusion

Xinfu Chen; Yuanwei Qi

2009-01-01

400

Biochemical Characterization of the Arabidopsis Biotin Synthase Reaction. The Importance of Mitochondria in Biotin Synthesis1  

PubMed Central

Biotin synthase, encoded by the bio2 gene in Arabidopsis, catalyzes the final step in the biotin biosynthetic pathway. The development of radiochemical and biological detection methods allowed the first detection and accurate quantification of a plant biotin synthase activity, using protein extracts from bacteria overexpressing the Arabidopsis Bio2 protein. Under optimized conditions, the turnover number of the reaction was >2 h?1 with this in vitro system. Purified Bio2 protein was not efficient by itself in supporting biotin synthesis. However, heterologous interactions between the plant Bio2 protein and bacterial accessory proteins yielded a functional biotin synthase complex. Biotin synthase in this heterologous system obeyed Michaelis-Menten kinetics with respect to dethiobiotin (Km = 30 ?m) and exhibited a kinetic cooperativity with respect to S-adenosyl-methionine (Hill coefficient = 1.9; K0.5 = 39 ?m), an obligatory cofactor of the reaction. In vitro inhibition of biotin synthase activity by acidomycin, a structural analog of biotin, showed that biotin synthase reaction was the specific target of this inhibitor of biotin synthesis. It is important that combination experiments using purified Bio2 protein and extracts from pea (Pisum sativum) leaf or potato (Solanum tuberosum) organelles showed that only mitochondrial fractions could elicit biotin formation in the plant-reconstituted system. Our data demonstrated that one or more unidentified factors from mitochondrial matrix (pea and potato) and from mitochondrial membranes (pea), in addition to the Bio2 protein, are obligatory for the conversion of dethiobiotin to biotin, highlighting the importance of mitochondria in plant biotin synthesis.

Picciocchi, Antoine; Douce, Roland; Alban, Claude

2001-01-01

401

Simulation of chemical reactions in solution by a combination of classical and quantum mechanical approach  

NASA Astrophysics Data System (ADS)

A classical trajectory mapping method was developed to study chemical reactions in solution and in enzymes. In this method, the trajectories were calculated on a classical potential surface and the free energy profile was obtained by mapping the classical surface to the quantum mechanical surface obtained by the semiempirical AM1 method. There is no need to perform expensive quantum mechanical calculations at each iteration step. This method was applied to proton transfer reactions both in aqueous solution and in papain. The results are encouraging, indicating the applicability of this hybrid method to chemical reactions both in solution and in enzymes.

Onida, Giovanni; Andreoni, Wanda

1995-09-01

402

KEMOD: A mixed chemical kinetic and equilibrium model of aqueous and solid phase geochemical reactions  

SciTech Connect

This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.

Yeh, G.T.; Iskra, G.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil Engineering; Szecsody, J.E.; Zachara, J.M.; Streile, G.P. [Pacific Northwest Lab., Richland, WA (United States)

1995-01-01

403

Effect of absolute laser phase on reaction paths in laser-induced chemical reactions  

SciTech Connect

Potential surfaces, dipole moments, and polarizabilities are calculated by ab initio methods [unrestricted MP2(full)/6-311++G(2d,2p)] along the reaction paths of the F+CH{sub 4} and Cl+CH{sub 4} reaction systems. It is found that in general dipole moments and polarizabilities exhibit peaks near the transition state. In the case of X=F these peaks are on the products side and in the case of X=Cl they are on the reactants side indicating an early transition state in the case of fluorine and a late transition state in the case of chlorine. An analysis of the geometric changes along the reaction paths reveals a one-to-one correspondence between the peaks in the electric properties and peaks in the rate of change of certain internal geometric coordinates along the reaction path. Interaction with short infrared intense laser fields pulses leads to the possibility of interferences between the dipole and polarizability laser-molecule interactions as a function of laser phase. The larger dipole moment in the Cl+CH{sub 4} reaction can lead to the creation of deep wells (instead of energy barriers) and new strongly bound states in the transition state region. This suggests possible coherent control of the reaction path as a function of the absolute phase of the incident field, by significant modification of the potential surfaces along the reaction path and, in particular, in the transition state region.

Bandrauk, Andre D.; Sedik, El-Wallid S.; Matta, Cherif F. [Laboratoire de Chimie Theorique, Faculte des Sciences, Universite de Sherbrooke, Sherbrooke, Quebec J1K 2R1 (Canada); Lash Miller Chemical Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6 (Canada)

2004-10-22

404

Force-activated reactivity switch in a bimolecular chemical reaction at the single molecule level  

NASA Astrophysics Data System (ADS)

Mechanical force is a distinct and usually less explored way to activate chemical reaction because it can deform the reacting molecules along a well-defined direction of the reaction coordinate. However, the effect of mechanical force on the free- energy surface that governs a chemical reaction is still largely unknown. The combination of protein engineering with single-molecule force-clamp spectroscopy allows us to study the influence of mechanical force on the rate at which a protein disulfide bond is reduced by some reducing agents in a bimolecular substitution reaction (so-called SN2). We found that cleavage of a protein disulfide bond by hydroxide anions exhibits an abrupt reactivity ``switch'' at 500 pN, after which the accelerating effect of force on the rate of an SN2 chemical reaction greatly diminishes. We propose that an abrupt force- induced conformational change of the protein disulfide bond shifts its ground state, drastically changing its reactivity in SN2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule. References: S. Garcia-Manyes, J. Liang, R. Szoszkiewicz, T-L. Kuo and J. M. Fernandez, Nature Chemistry, 1, 236-242, 2009.

Szoszkiewicz, Robert; Garcia-Manyes, Sergi; Liang, Jian; Kuo, Tzu-Ling; Fernandez, Julio M.

2009-10-01

405

Chemical alterations taken place during deep-fat frying based on certain reaction products: a review.  

PubMed

Deep-fat frying at 180 °C or above is one of the most common food processing methods used for preparing of human kind foods worldwide. However, a serial of complex reactions such as oxidation, hydrolysis, isomerization, and polymerization take place during the deep-fat frying course and influence quality attributes of the final product such as flavor, texture, shelf life and nutrient composition. The influence of these reactions results from a number of their products including volatile compounds, hydrolysis products, oxidized triacylglycerol monomers, cyclic compounds, trans configuration compounds, polymers, sterol derivatives, nitrogen- and sulphur-containing heterocyclic compounds, acrylamide, etc. which are present in both frying oil and the fried food. In addition, these reactions are interacted and influenced by various impact factors such as frying oil type, frying conditions (time, temperature, fryer, etc.) and fried material type. Based on the published literatures, three main organic chemical reaction mechanisms namely hemolytic, heterolytic and concerted reaction were identified and supposed to elucidate the complex chemical alterations during deep-fat frying. However, well understanding the mechanisms of these reactions and their products under different conditions helps to control the deep-fat frying processing; therefore, producing healthy fried foods. By means of comprehensively consulting the papers which previously studied on the chemical changes occurred during deep-fat frying process, the major reaction products and corresponding chemical alterations were reviewed in this work. PMID:22800882

Zhang, Qing; Saleh, Ahmed S M; Chen, Jing; Shen, Qun

2012-07-16

406

Kinetics of sulphuric alkylation reactions: study of two reaction steps and modelling using chemical families grouping.  

National Technical Information Service (NTIS)

Isobutane/olefins sulphuric alkylation is used in the petroleum industry to prepare fuels with high octane numbers. Although the alkylation reaction/process has been considered by numerous investigators, relatively few results have been published concerni...

L. E. Pizarro Borges

1995-01-01

407

Direct imaging of covalent bond structure in single-molecule chemical reactions.  

PubMed

Observing the intricate chemical transformation of an individual molecule as it undergoes a complex reaction is a long-standing challenge in molecular imaging. Advances in scanning probe microscopy now provide the tools to visualize not only the frontier orbitals of chemical reaction partners and products, but their internal covalent bond configurations as well. We used noncontact atomic force microscopy to investigate reaction-induced changes in the detailed internal bond structure of individual oligo-(phenylene-1,2-ethynylenes) on a (100) oriented silver surface as they underwent a series of cyclization processes. Our images reveal the complex surface reaction mechanisms underlying thermally induced cyclization cascades of enediynes. Calculations using ab initio density functional theory provide additional support for the proposed reaction pathways. PMID:23722428

de Oteyza, Dimas G; Gorman, Patrick; Chen, Yen-Chia; Wickenburg, Sebastian; Riss, Alexander; Mowbray, Duncan J; Etkin, Grisha; Pedramrazi, Zahra; Tsai, Hsin-Zon; Rubio, Angel; Crommie, Michael F; Fischer, Felix R

2013-05-30

408

Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents  

NASA Astrophysics Data System (ADS)

We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.

Dzhioev, Alan A.; Kosov, Daniel S.; von Oppen, Felix

2013-04-01

409

Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents.  

PubMed

We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom. PMID:23574204

Dzhioev, Alan A; Kosov, Daniel S; von Oppen, Felix

2013-04-01

410

Chemical reactions in a scramjet combustor and two-dimensional nozzles  

NASA Astrophysics Data System (ADS)

Finite-rate chemistry of hydrogen-air combustion is to be investigated numerically in a one-dimensional constant pressure SCRAMJET combustor and two-dimensional nozzles. Detailed reaction mechanisms and temperature dependent thermodynamics are to be used in the models. The aspects of interest include the combustion characteristics at different fuel-air ratios, pressures and initial temperatures in the combustor. Methods for enhancing the combustion rate in the combustor is to be studied also. The effect of expansion rate on the hydrogen-air reactions is the prime focus of the nozzle calculation. The results from different inlet conditions and wall geometries are to be analyzed. A computer model for a one-dimensional (channel-flow) combustor is constructed based on the chemical kinetics subroutine library CHEMKIN. Subsequent calculations show that the initial temperature is the most important parameter in the combustor. It is further discovered that certain reaction steps are responsible for the initial delay exhibited in all hydrogen-air combustion processes. Low temperature behavior is studied extensively and augmentation methods are developed. The introduction of a small percentage of the hydrogen radical into the initial mixture is found to be the most effective in reducing the reaction delay. The combustor pressure enters the overall reaction process in a linear manner. The calculations over five combustor pressures show that the initial delay in hydrogen-air reaction and the following period of explosion are proportional to the combustor pressure raised to certain powers. The nozzle model is two-dimensional, steady and inviscid with no conductivity and diffusivity. Two schemes are developed to handle the boundary conditions. One is based on pure numerical interpolation/extrapolation methods while the other imposes analytical supersonic characteristic equations. The former scheme is found to be more efficient while the latter is more accurate. In analysing the response of the combustion product to an expansion, it is found that the formation of water is favoured by an expansion. A closer examination reveals that the behavior can be attributed to the abundance of free radicals in the nozzle inlet composition. Freezing is not clearly observed except for the NO_x species.

Yeung, Moon-Tai

411

SCRIPDB: a portal for easy access to syntheses, chemicals and reactions in patents  

PubMed Central

The patent literature is a rich catalog of biologically relevant chemicals; many public and commercial molecular databases contain the structures disclosed in patent claims. However, patents are an equally rich source of metadata about bioactive molecules, including mechanism of action, disease class, homologous experimental series, structural alternatives, or the synthetic pathways used to produce molecules of interest. Unfortunately, this metadata is discarded when chemical structures are deposited separately in databases. SCRIPDB is a chemical structure database designed to make this metadata accessible. SCRIPDB provides the full original patent text, reactions and relationships described within any individual patent, in addition to the molecular files common to structural databases. We discuss how such information is valuable in medical text mining, chemical image analysis, reaction extraction and in silico pharmaceutical lead optimization. SCRIPDB may be searched by exact chemical structure, substructure or molecular similarity and the results may be restricted to patents describing synthetic routes. SCRIPDB is available at http://dcv.uhnres.utoronto.ca/SCRIPDB.

Heifets, Abraham; Jurisica, Igor

2012-01-01

412

Electric field suppression of ultracold confined chemical reactions  

SciTech Connect

We consider ultracold collisions of polar molecules confined in a one-dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking {sup 40}K{sup 87}Rb molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes for KRb molecules to be 1 s. We find a ratio of elastic to quenching collision rates of about 100, which may be sufficient to achieve efficient evaporative cooling of polar KRb molecules.

Quemener, Goulven; Bohn, John L. [JILA, NIST and University of Colorado, Boulder, Colorado 80309-0440 (United States)

2010-06-15

413

From chemical reactions to evolution: Emergence of species  

NASA Astrophysics Data System (ADS)

The Chemoton model constitutes a minimalistic description of a protocell unit. The original formulation assumes three coupled chemical networks, representing a proto-metabolism, a template duplication and the membrane growth. An improved version is here proposed that explicitly incorporates the effects of the volume changes, due to the membrane growth. A stochastic mechanism is also introduced that mimics a stochastic source of error in the template duplication process. Numerical simulations are performed to monitor the time evolution of a family of protocells, under the chemoton hypothesis. An open-ended Darwinian evolution under the pressure of the environment is reproduced thus allowing to conclude that differentiation into species is an emergent property of the model.

Carletti, T.; Fanelli, D.

2007-01-01

414

Numerical Modeling of Coupled Variably-Saturated Fluid Flow and Reactive Transport with Fast and Slow Chemical Reactions  

SciTech Connect

The couplings among chemical reaction rates, advective and diffusive transport in fractured media or soils, and changes in hydraulic properties due to precipitation and dissolution within fractures and in rock matrix are important for both nuclear waste disposal and remediation of contaminated sites. This paper describes the development and application of LEHGC2.0, a mechanistically-based numerical model for simulation of coupled fluid flow and reactive chemical transport including both fast and slow reactions invariably saturated media. Theoretical bases and numerical implementations are summarized, and two example problems are demonstrated. The first example deals with the effect of precipitation-dissolution on fluid flow and matrix diffusion in a two-dimensional fractured media. Because of the precipitation and decreased diffusion of solute from the fracture into the matrix, retardation in the fractured medium is not as large as the case wherein interactions between chemical reactions and transport are not considered. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions.

LI, MING-HSU; SIEGEL, MALCOLM D.; YEH, GOUR-TSYH (GEORGE)

1999-09-20

415

Numerical modeling of coupled variably saturated fluid flow and reactive transport with fast and slow chemical reactions.  

PubMed

The couplings among chemical reaction rates, advective and diffusive transport in fractured media or soils, and changes in hydraulic properties due to precipitation and dissolution within fractures and in rock matrix are important for both nuclear waste disposal and remediation of contaminated sites. This paper describes the development and application of LEHGC2.0, a mechanistically based numerical model for simulation of coupled fluid flow and reactive chemical transport, including both fast and slow reactions in variably saturated media. Theoretical bases and numerical implementations are summarized, and two example problems are demonstrated. The first example deals with the effect of precipitation/dissolution on fluid flow and matrix diffusion in a two-dimensional fractured media. Because of the precipitation and decreased diffusion of solute from the fracture into the matrix, retardation in the fractured medium is not as large as the case wherein interactions between chemical reactions and transport are not considered. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions. PMID:11288590

Yeh, G T; Siegel, M D; Li, M H

2001-02-01

416

Electronically excited molecules: Reaction kinetics and emission of light: Nanosecond infrared spectroscopy, electronic emission from chemical reactions  

Microsoft Academic Search

A time-resolved IR absorption spectrometer capable of detecting chemical transients on the nanosecond timescale was designed, constructed, and successfully implemented. The spectrometer was used to characterize the vibrational relaxation of an open shell radical species, CF3, produced with excess energy from the photolysis of the parent CF3I compound. The effects of vibrational excitation in the CF3 radical on the reaction

C. B. Moore

1992-01-01

417

Small-angle neutron scattering studies of chemical reaction and reaction-induced self-assembly  

NASA Astrophysics Data System (ADS)

We have investigated a self-assembling process of cellulose artificially synthesized via enzymatic polymerization by means of in-situ and time-resolved small-angle neutron scattering (SANS). The results elucidated the following: (i) cellulose molecules were synthesized at a special reaction site of the enzyme (cellulase) located on or near the smooth surface of the self-assembled enzymes formed in the reaction medium; (ii) the synthesized molecules associated themselves via diffusion-limited aggregation (DLA) and crystallized into fibrils and (iii) the fibrils formed the aggregates, which had the surface fractal dimension Ds increasing from 2 to 2.3 with the reaction time, on the smooth surface of the enzyme aggregates.

Tanaka, H.; Koizumi, S.; Hashimoto, T.; Kurosaki, K.; Ohmae, M.; Kobayashi, S.

2006-11-01

418

Influence of reaction heat on time dependent processes in a chemically reacting binary mixture  

NASA Astrophysics Data System (ADS)

In this paper we study time dependent problems, like the propagation of sound waves or the behavior of small local wave disturbances induced by spontaneous internal fluctuations, in a binary mixture undergoing a chemical reaction of type A + A ? B + B. The study is developed at the hydrodynamic Euler level, in a chemical regime of fast reactive process in which the chemical reaction is close to its final equilibrium state. The hydrodynamic state of the mixture is described by the balance equations for the mass densities of both constituents A and B, together with the conservation laws for the momentum and total energy of the mixture. The progress of the chemical reaction is specified by an Arrhenius-type reaction rate which defines the net balance between production and consumption of each constituent. Assuming that the considered time dependent problems induce weak macroscopic deviations, the hydrodynamic equations are linearized through a normal mode expansion of the state variables around the equilibrium state. From the dispersion relation of the normal modes, we determine the free and forced phase velocities as well as the attenuation coefficients of the waves. We show that the dispersion and absorption of these waves depend explicitly on the heat of the chemical reaction, the concentrations of the constituents and the activation energy through the exponential factor of Arrhenius law.

Marques, Wilson, Jr.; Kremer, Gilberto M.; Soares, Ana Jacinta

2012-11-01

419

Changes in mechanical property of sandstone by chemical reaction  

Microsoft Academic Search

The effect of increasing temperature on the hydro-mechanical properties of rocks is a highly important topic. When we select a site for underground excavation for the disposal of high-level radioactive waste and CO2-underground storage, it is necessary to know the effects of temperature and confining pressure with water, called the deep geological environment. In fact increasing temperatures cause micro-cracking and

T. Takemura; M. Manaka; M. Takahashi

2006-01-01

420

Mixing and chemical reaction in an idealized swirl chamber  

SciTech Connect

A vorticity-based, low-Mach-number model for simulating combustion in closed chambers is constructed. Numerical scheme is based on a mixed finite-difference pseudo-spectral discretization of the governing equations. Discrete evolution equations are integrated in time using a predictor-corrector scheme, while discrete elliptic systems are inverted with the help of fast-Poisson solver. Scheme is applied to analyze mixing and combustion in an idealized swirl cavity, which consists of the annular space between a spinning inner cylinder and a stationary reaction. To this end, we assume that the oxidizer and fuel are initially separated by a thin mixed region, and carefully control mixing levels by varying the duration of the swirl-driven mixing period. The mixture is then ignited along the boundary of the inner cylinder. When pre-mixing is complete, an axisymmetric flame front is established, and the reactants are consumed as the front propagates radially outwards. When the charge is partially mixed, combustion in the early stages predominantly occurs within a non-uniform premixed front. As this non-uniform front approaches the outer cylinder, a transition to a distributed combustion regime occurs. Following the transition, the remaining fuel burns at a slow rate within non-premixed flames which wrap around the inner cylinder. Results show that the mixing time has substantial effects on the pressure rise within the cavity and on the evolution of the burnt fraction, and that these effects become more pronounced as the Damkoehler number increases.

Knio, O.M.; Worlikar, A.S. [Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Mechanical Engineering; Najm, H.N. [Sandia National Labs., Livermore, CA (United States)

1996-01-01

421

Strength of Reaction Runaway in Free Radical Polymerization: Competition between Diffusion-Controlled and Chemically-Controlled Reactions  

NASA Astrophysics Data System (ADS)

Free radical polymerization (FRP) exhibits autoacceleration or reaction runaway, the magnitude of which depends on polymer molecular weight (MW) and species. Autoacceleration in methyl methacrylate (MMA) FRP may be understood from the fact that the concentration dependence of the termination rate parameter scales with the concentration dependence of the diffusion coefficient of the "average short chain" participating in the polymer-polymer termination reaction. However, FRP of other monomers exhibits a weak runaway indicative of a competition between diffusion-controlled termination and chemically-controlled chain transfer. Analysis of this competition in styrene and other FRP systems (and the lack thereof in MMA) is made from studies of polymer self-diffusion via PFG-NMR, diffusion-limited interaction rates via phosphorescence quenching, and overall reaction rates. Differences in polydispersity and MW expected from termination by combination versus dead polymer production from chain transfer will be tested by cumulative/differential analysis of MW distributions.

Chekal, Brian P.; Emrani, Mehdi; Torkelson, John M.

2001-03-01

422

Supercritical fluid phase separations induced by chemical reactions  

SciTech Connect

Our statistical mechanical studies predict that a chemically reactive system containing species composed of C, H, N, O atoms can exhibit a phase separation into a N{sub 2}-rich and a N{sub 2}-poor phase. The preset work is concerned with the effect of the fluid phase separation upon addition of F atoms in the system. Our study shows that F atoms mainly appear as a constituent of HF in a N{sub 2}-poor fluid phase up to a certain pressure beyond which they occur as CF{sub 4} in a N{sub 2}-rich phase and that the phase separation may be abrupt in thermodynamic sense. The pressure at the phase boundary can occur at about 30 GPa at 3000 K and about 10 GPa to 20 GPa at 1000 K.Some of these ranges maybe accessible by present-day experimental high-pressure techniques. We discuss implications of this study to detonation physics.

Ree, F.H.; Viecelli, J.A.; van Thiel, M.

1997-11-01

423

Computed potential energy surfaces for chemical reactions. Semiannual report, 1 January-30 June 1990  

SciTech Connect

The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

Walch, S.P.

1990-01-01

424

The hydrogen atom, hydrogen molecule exchange reaction: Experimental evidence for dynamical resonances in chemical reactions  

NASA Astrophysics Data System (ADS)

The hydrogen exchange reaction, H + H2 --> H2 + H, and its isotopic variants are considered to be the simplest of all bimolecular reactions. Quasibound collision complexes (dynamic resonances) have been predicted to play a role in this reaction since 1971, but experimental observation of these effects has been achieved only recently. We co-expand a mixture of HBr and D2 into a vacuum chamber and initiate the reaction H + D2 --> HD + D by photolyzing HBr with a laser pulse. Approximately 15 nanoseconds after initiating the reaction we ionize the HD(v', j') products with a second laser pulse. We detect the HD+ ions with a time-of-flight mass spectrometer that allows us to measure the amount of a particular HD(v ', j') product state as well as the distribution of its lab-frame speeds. Because the reaction is initiated via the photolysis of HBr, we can control the center-of-mass collision energy by changing the wavelength of the photolysis laser. From these measurements we construct energy-dependent distributions of product states (relative integral cross sections) and distributions of scattering angles for individual states (differential cross sections). Differential and integral cross sections were measured for H + D 2 --> HD(v' = 1-3, j') + D reactions at collision energies near 1.6 eV. The cross section measurements for the HD(v' = 1,2) products agree with a simple hard-sphere model, however the results for the HD(v' = 3) products deviate from predictions. These deviations are most notable in the differential cross sections of the HD(v' = 3, j' = 0,1) products where forward scattering is prominent. Quasiclassical trajectory calculations suggest that this forward scattering is the result of a short-lived collision complex (Feshbach resonance). This interpretation is reinforced with a series of HD(v' = 3, j' = 0) experimental differential cross sections spanning 1.39-1.75 eV in which the forward scattered portion is observed to rise and fall as a function of collision energy. The observed peak can be fit to a Lorentzian line shape having a full width at half maximum (FWHM) of 0.07 eV. This FWHM suggests a collision complex lifetime on the order of 10 fs, far too short for the rotation of the H-D-D complex.

Bean, Brian David

2000-09-01

425

The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research  

SciTech Connect

Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

Westbrook, C K; Pitz, W J; Curran, H J; Mehl, M

2008-07-16

426

Assessing solvation effects on chemical reactions with globally optimized solvent clusters.  

PubMed

We have examined the influence of water solvent on the Menshutkin reaction of methyl chloride with ammonia by performing static, quantum chemical calculations. We have employed large, explicit, and globally structure-optimized water clusters around the reaction center, in a mixed explicit/implicit solvent model. This approach deliberately deviates from attempts to capture the most likely solvent-molecule distribution around a reaction center. Instead, it explores extremes on the scale of rearrangement speed in terms of the surrounding solvent cluster, relative to the reaction progress itself. A comparison to traditional theoretical and experimental results enables us to quantify the energy penalty that is induced by the inability of the water cluster to instantaneously and completely follow the reaction progress. In addition, the influence of water clusters on the reaction energy profile can be much larger than merely changing it somewhat. Certain clusters can completely annihilate the sizeable activation barrier of 23.5 kcal?mol(-1) . PMID:23824779

Li, Yan; Hartke, Bernd

2013-07-03

427

Coupling quantum interpretative techniques: another look at chemical mechanisms in organic reactions.  

PubMed

A cross ELF-NCI analysis is tested over prototypical organic reactions. The synergetic use of ELF and NCI enables the understanding of reaction mechanisms since each method can respectively identify regions of strong and weak electron pairing. Chemically intuitive results are recovered and enriched by the identification of new features. Non covalent interactions are found to foresee the evolution of the reaction from the initial steps. Within NCI, no topological catastrophe is observed as changes are continuous to such an extent that future reaction steps can be predicted from the evolution of the initial NCI critical points. Indeed, strong convergences through the reaction paths between ELF and NCI critical points enable to identify key interactions at the origin of the bond formation. VMD scripts enabling the automatic generation of movies depicting the cross NCI/ELF analysis along a reaction path (or following a Born-Oppenheimer molecular dynamics trajectory) are provided as S.I. PMID:23185140

Gillet, Natacha; Chaudret, Robin; Contreras-Garc?a, Julia; Yang, Weitao; Silvi, Bernard; Piquemal, Jean-Philip

2012-09-18

428

Is there a motivation for a universal behaviour in molecular populations undergoing chemical reactions?  

PubMed

Many chemical reactions demonstrate a very similar evolution of reagent concentrations in time, although their species are quite different. This can be linked with a universal stochastic behavior of reagents. In this paper we show what role in understanding chemical kinetics stochastic models play. To support this concept, we consider two interesting cases known in the literature as first- and second-order reactions. The former has a stretched exponential decay in time for its reagent concentration, and the latter evolves hyperbolically. We have established that the behavior can be explained by limit theorems of probability theory. The reaction evolution is directly connected with different behavior motivations in reagent populations. The reason for the universal kinetics is found in the indices of the corresponding probability distribution functions. They are macroscopic parameters measured in chemical experiments. Such an approach allows ones to discover what happens with molecular populations in microscopic dynamics. PMID:23942846

Stanislavsky, A; Weron, K

2013-10-01

429

On the curvature in logarithmic plots of rate coefficients for chemical reactions  

PubMed Central

In terms of the reduced potential energy barrier ? = ?uTS/kT, the rate coefficients for chemical reactions are usually expressed as proportional to e-?. The coupling between vibrational modes of the medium to the reaction coordinate leads to a proportionality of the regularized gamma function of Euler Q(a,?) = ?(a,?)/?(a), with a being the number of modes coupled to the reaction coordinate. In this work, the experimental rate coefficients at various temperatures for several chemical reactions were fitted to the theoretical expression in terms of Q(a,?) to determine the extent of its validity and generality. The new expression affords lower deviations from the experimental points in 29 cases out of 38 and it accounts for the curvature in the logarithmic plots of rate coefficients versus inverse temperature. In the absence of tunneling, conventional theories predict the curvature of these plots to be identically zero.

2011-01-01

430

Stereodynamics of chemical reactions: quasi-classical, quantum and mixed quantum-classical theories  

NASA Astrophysics Data System (ADS)

In this review, some benchmark works by Han and coworkers on the stereodynamics of typical chemical reactions, triatomic reactions H + D2, Cl + H2 and O + H2 and polyatomic reaction Cl+CH4/CD4, are presented by using the quasi-classical, quantum and mixed quantum-classical methods. The product alignment and orientation in these A+BC model reactions are discussed in detail. We have also compared our theoretical results with experimental measurements and demonstrated that our theoretical results are in good agreement with the experimental results. Quasi-classical trajectory (QCT) method ignores some quantum effects like the tunneling effect and zero-point energy. The quantum method will be very time-consuming. Moreover, the mixed quantum-classical method can take into account some quantum effects and hence is expected to be applicable to large systems and widely used in chemical stereodynamics studies.

Xu, Wenwu; Zhao, Guangjiu

2012-04-01

431

Stereodynamics of chemical reactions: quasi-classical, quantum and mixed quantum-classical theories  

NASA Astrophysics Data System (ADS)

In this review, some benchmark works by Han and coworkers on the stereodynamics of typical chemical reactions, triatomic reactions H + D2, Cl + H2 and O + H2 and polyatomic reaction Cl+CH4/CD4, are presented by using the quasi-classical, quantum and mixed quantum-classical methods. The product alignment and orientation in these A+BC model reactions are discussed in detail. We have also compared our theoretical results with experimental measurements and demonstrated that our theoretical results are in good agreement with the experimental results. Quasi-classical trajectory (QCT) method ignores some quantum effects like the tunneling effect and zero-point energy. The quantum method will be very time-consuming. Moreover, the mixed quantum-classical method can take into account some quantum effects and hence is expected to be applicable to large systems and widely used in chemical stereodynamics studies.

Xu, Wenwu; Zhao, Guangjiu

2011-12-01

432

An in-situ combustion reservoir simulator with a new representation of chemical reactions  

SciTech Connect

Numerical simulation of in-situ combustion processes poses numerical problems related to the representation of chemical reactions in the burning zone. This paper presents a new approach to the description of the combustion front. The fully implicit thermal compositional model developed to simulate oil recovery by wet or dry forward combustion is formulated to handle three dimensions, three phases, gravity and capillary forces, heat transfer by convection and conduction within the reservoir, and conductive heat loss to adjacent strata. Two options are available. The first includes four components and one fuel combustion reaction., The second allows any number of components and several reactions. The first option emphasizes description of the combustion front with a new formulation that uses a heat-release curve to improve numerical stability and to give accurate temperature distribution with large gridblocks. The paper compares different representations of chemical reactions and includes results of a sensitivity study on the mesh size.

Le Thiez, P.A.; Lemonnier, P.A. (Inst. Francais du Petrole (FR))

1990-08-01

433

Chemical reactions and nitrogen oxide emissions in bluff-body stabilized flames  

NASA Astrophysics Data System (ADS)

The objectives of this thesis are the investigation of the characteristics of partially premixed disk-stabilized flames. Among them, chemical reaction and NO/NOx emission in partially premixed disk-stabilized flame are the main topics. The present work includes experimental studies and numerical modelling. An intensive experimental investigation been carried out to study the characteristics of chemical reaction, NO/NOx emissions and visual characteristics of a partially premixed bluff-body stabilized flame. In order to understand better the mechanism of chemical reaction and the NOx, formation of the flame, two factors, the Spatial Reaction Index (SRI) and the Modified Mixture Fraction (MMF), have been established respectively. A numerical model for the disk-stabilized flame, which provided the information about its detailed chemical reactions and NOx formation by burning butane in air, has been developed. Predictions obtained by using the model were compared with the experimental results. By carrying out the preset experimental and numerical studies, I have made the following contributions towards a better understanding of the partially premixed bluff body stabilized flame. (1) A non-traditional approach, the image-processing technique, has been applied to analyze the visual characteristics of the partially premixed disk-stabilized flame. (2) The present experimental results provide an excellent database for predicting the NO/NOx formation mechanisms in the disk-stabilized flame. (3) A Spatial Reaction Index (SRI), which is the ratio of O2 chemical reaction rate to O2 mass transfer rate, based on the present experimental results has been proposed. (4) A Modified Mixture Fraction (MMF), which is the mess ratio of the carbon containing species to all gaseous species, has also been proposed based on the present experimental findings. (5) A numerical model of the disk-stabilized flame, which is based on the calculation codes of a Perfect Stirred Reactor, has been developed. (Abstract shortened by UMI.)

Shen, Hong Mei

2001-07-01

434

Visible chemical lasers: Reactions of metastable oxygen and the study of the red yoshida reaction  

Microsoft Academic Search

During the period covered by the U.S. Air Force Grant we have identified the CuCl2 molecule as responsible for the I.R. and strong red emission in the 'Yoshida reaction.' The deep potential well of the CuCl2 ground state favors population inversion in the two involved excited states ((sup 2)delta(sub g) and (sup 2)Pi(sub u)). The lifetime of the highest excited

Roger Bacis

1992-01-01

435

Slow Hydrogen Transfer Reactions of Oxo-- and Hydroxo-- Vanadium Compounds: the Importance of Intrinsic Barriers  

PubMed Central

Reactions are described that interconvert vanadium(IV) oxo-hydroxo complexes [VIVO(OH)(R2bpy)2]BF4 (1a-c) and vanadium(V) dioxo complexes [VVO2(R2bpy)2]BF4 (2a-c) [R2bpy = 4,4?-di-t-butyl-2,2?-bipyridine (tBu2bpy), a; 4,4?-dimethyl-2,2?-bipyridine (Me2bpy), b; 2,2?-bipyridine (bpy), c]. These are rare examples of pairs of isolated, sterically unencumbered, first-row metal-oxo/hydroxo complexes that differ by a hydrogen atom (H+ + e?). The VIV– tBu2bpy derivative 1a has a useful 1H NMR spectrum, despite being paramagnetic. Complex 2a abstracts H• from organic substrates with weak O–H and C–H bonds, converting 2,6-tBu2-4-MeO-C6H2OH (ArOH) and 2,2,6,6-tetramethyl-N-hydroxy-piperidine (TEMPOH) to their corresponding radicals ArO• and TEMPO, hydroquinone to benzoquinone, and dihydroanthracene to anthracene. The equilibrium constant for 2a + ArOH ? 1a + ArO• is (4 ± 2) × 10?3, implying that the VO–H bond dissociation free energy (BDFE) is 70.6 ± 1.2 kcal mol?1. Consistent with this value, 1a is oxidized by 2,4,6-tBu3C6H2O•. All of these reactions are surprisingly slow, typically occurring over hours at ambient temperatures. The net hydrogen-atom pseudo-self-exchange 1a + 2b ? 2a + 1b, using the tBu- and Me-bpy substituents as labels, also occurs slowly, with kse = 1.3 × 10?2 M?1 s?1 at 298 K, ?H‡ = 15 ± 2 kcal mol?1, and ?S‡= 16 ± 5 cal mol?1 K. Using this kse and the BDFE, the vanadium reactions are shown to follow the Marcus cross relation moderately well, with calculated rate constants within 102 of the observed values. The vanadium self-exchange reaction is ca. 106 slower than that for the related RuIVO(py)(bpy)22+ / RuIIIOH(py)(bpy)22+ self-exchange. The origin of this dramatic difference has been probed with DFT calculations on the self-exchange reactions of 1c + 2c and on mono-cationic ruthenium complexes with pyrrolate or fluoride in place of the py ligands. The calculations reproduce the difference in barrier heights and show that transfer of a hydrogen atom involves more structural reorganization for vanadium than the Ru analogs. The vanadium complexes have larger changes in the metal–oxo and metal–hydroxo bond lengths, which is traced to the difference in d-orbital occupancy in the two systems. This study thus highlights the importance of intrinsic barriers in the transfer of a hydrogen atom, in addition to the thermochemical (bond strength) factors that have been previously emphasized.

Waidmann, Christopher R.; Zhou, Xin; Tsai, Erin A.; Kaminsky, Werner; Hrovat, David A.; Borden, Weston Thatcher; Mayer, James M.

2009-01-01

436

Child-Rearing Practices toward Children with Hemophilia: The Relative Importance of Clinical Characteristics and Parental Emotional Reactions.  

ERIC Educational Resources Information Center

Addresses the relative importance of clinical characteristics of the child and parental emotional reactions, to child-rearing practices towards children with hemophilia. Results indicate that mother's emotional reactions appear to have a stronger influence on child-rearing uncertainty and overprotection than clinical characteristics of the child.…

Banis, S.; Suurmeijer, Th. P. B. M.; van Peer, D. R.

1999-01-01

437

An ES-BGK model for a gas mixture with bimolecular chemical reaction  

NASA Astrophysics Data System (ADS)

A relaxation-time-approximation of a Boltzmann kinetic model for a slow bimolecular chemical reaction in a collision dominated gas mixture is presented. The dominant mechanical collision operator, approximated by an ellipsoidal BGK operator recently introduced in the literature, is coupled to a kinetic relaxation model enforcing chemical equilibrium. The hydrodynamic limit up to the fluid-dynamic reactive Navier-Stokes equations are worked out by a Chapman-Enskog asymptotic procedure, emphasizing reactive effects in the resulting reaction-diffusion transport equations.

Groppi, M.; Spiga, G.

2012-11-01

438

Non-invasive estimation of dissipation from non-equilibrium fluctuations in chemical reactions  

NASA Astrophysics Data System (ADS)

We show how to extract an estimate of the entropy production from a sufficiently long time series of stationary fluctuations of chemical reactions. This method, which is based on recent work on fluctuation theorems, is direct, non-invasive, does not require any knowledge about the underlying dynamics and is applicable even when only partial information is available. We apply it to simple stochastic models of chemical reactions involving a finite number of states, and for this case, we study how the estimate of dissipation is affected by the degree of coarse-graining present in the input data.

Muy, S.; Kundu, A.; Lacoste, D.

2013-09-01

439

THE LIFETIME OF AEROSOLS IN AMBIENT AIR: CONSIDERATION OF THE EFFECTS OF SURFACTANTS AND CHEMICAL REACTIONS  

SciTech Connect

The relatively long lifetime of droplets in atmospheric haze and fog in comparison with similar droplets of pure water is attributed to the presence of a monolayer of surfactant film and to the accumulation Of soluble salts from chemical reactions. The lifetime of these droplets is a significant factor in the evaluation of the role of heterogeneous aqueous chemical reactions occurring in the troposphere. Several mechanisms of SO{sub 2} oxidation in the presence of liquid water are investigated. It is shown that soot-catalyzed oxidation of sulfur dioxide could be responsible for the high level of sulfate concentration observed in the coastal industrial areas.

Toossi, R.; Novakov, T.

1984-04-01

440

Effects of exothermic chemical reaction on the photoacoustic effect from particulate suspensions.  

PubMed

Irradiation of chemically reactive particulate suspensions by high power, pulsed laser radiation initiates reactions at the sites of the particles so that besides the absorbed optical energy, chemical energy is liberated. In addition to the release of chemical energy, chemical reaction can result in gas production both of which result in enhancement in the amplitude of the photoacoustic effect. Here we report photoacoustic and transient grating experiments with colloidal C in mixtures of H(2)O(2) with H(2)O. The inclusion of H(2)O(2) in an aqueous C suspension changes the normally endothermic reaction of C with H(2)O into the highly exothermic reaction of C with H(2)O(2) leading to both an enhanced photoacoustic effect and an increase in light emission from the suspension. As well, laser-initiated exothermic reactions in suspensions of C with CH(3)NO(2) and particulate Hg(CNO)(2) in H(2)O are shown to result in greatly enhanced photoacoustic signal amplitudes. PMID:21456682

Park, Han Jung; Wu, Binbin; Diebold, Gerald J

2011-03-28

441

Effects of exothermic chemical reaction on the photoacoustic effect from particulate suspensions  

NASA Astrophysics Data System (ADS)

Irradiation of chemically reactive particulate suspensions by high power, pulsed laser radiation initiates reactions at the sites of the particles so that besides the absorbed optical energy, chemical energy is liberated. In addition to the release of chemical energy, chemical reaction can result in gas production both of which result in enhancement in the amplitude of the photoacoustic effect. Here we report photoacoustic and transient grating experiments with colloidal C in mixtures of H2O2 with H2O. The inclusion of H2O2 in an aqueous C suspension changes the normally endothermic reaction of C with H2O into the highly exothermic reaction of C with H2O2 leading to both an enhanced photoacoustic effect and an increase in light emission from the suspension. As well, laser-initiated exothermic reactions in suspensions of C with CH3NO2 and particulate Hg(CNO)2 in H2O are shown to result in greatly enhanced photoacoustic signal amplitudes.

Park, Han Jung; Wu, Binbin; Diebold, Gerald J.

2011-03-01

442

Insights into the mechanism and catalysis of the native chemical ligation reaction.  

PubMed

Native chemical ligation of unprotected peptide segments involves reaction between a peptide-alpha-thioester and a cysteine-peptide, to yield a product with a native amide bond at the ligation site. Peptide-alpha-thioalkyl esters are commonly used because of their ease of preparation. These thioalkyl esters are rather unreactive so the ligation reaction is catalyzed by in situ transthioesterification with thiol additives. The most common thiol catalysts used to date have been either a mixture of thiophenol/benzyl mercaptan, or the alkanethiol MESNA. Despite the use of these thiol catalysts, ligation reactions typically take 24-48 h. To gain insight into the mechanism of native chemical ligaton and in order to find a better catalyst, we investigated the use of a number of thiol compounds. Substituted thiophenols with pK(a) > 6 were found to best combine the ability to exchange rapidly and completely with thioalkyl esters, and to then act as effective leaving groups in reaction of the peptide-thioester with the thiol side chain of a cysteine-peptide. A highly effective and practical catalyst was (4-carboxylmethyl)thiophenol ('MPAA'), a nonmalodorous, water-soluble thiol. Use of MPAA gave an order of magnitude faster reaction in model studies of native chemical ligation and in the synthesis of a small protein, turkey ovomucoid third domain (OMTKY3). MPAA should find broad use in native chemical ligation and in the total synthesis of proteins. PMID:16704265

Johnson, Erik C B; Kent, Stephen B H

2006-05-24

443

Force-activated reactivity switch in a bimolecular chemical reaction at the single molecule level  

NASA Astrophysics Data System (ADS)

Mechanical force can deform the reacting molecules along a well-defined direction of the reaction coordinate. However, the effect of mechanical force on the free-energy surface that governs a chemical reaction is still largely unknown. The combination of protein engineering with single-molecule AFM force-clamp spectroscopy allows us to study the influence of mechanical force on the rate at which a protein disulfide bond is reduced by some reducing agents in a bimolecular substitution reaction (so-called SN2). We found that cleavage of a protein disulfide bond by hydroxide anions exhibits an abrupt reactivity ``switch'' at 500 pN, after which the accelerating effect of force on the rate of an SN2 chemical reaction greatly diminishes. We propose that an abrupt force-induced conformational change of the protein disulfide bond shifts its ground state, drastically changing its reactivity in SN2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule. References: Sergi Garcia-Manyes, Jian Liang, Robert Szoszkiewicz, Tzu-Ling Kuo and Julio M. Fernandez, Nature Chemistry, 1, 236-242, 2009.

Szoszkiewicz, Robert; Garcia-Manyes, Sergi; Liang, Jian; Kuo, Tzu-Ling; Fernandez, Julio M.

2010-03-01

444

Dynamics of a vertically falling film in the presence of a first-order chemical reaction  

Microsoft Academic Search

The evolution of a vertically falling film in the presence of a simple first-order (exothermic or endothermic) chemical reaction is considered. The heat of reaction sets up surface tension gradients that induce thermocapillary stresses on the free-surface, thus affecting the evolution of the film. By using a long-wave expansion of the equations of motion and associated boundary conditions, we derive

Philip M. J. Trevelyan; Serafim Kalliadasis; John H. Merkin; Stephen K. Scott

2002-01-01

445

The plakotenins: biomimetic Diels-Alder reactions, total synthesis, structural investigations, and chemical biology.  

PubMed

The total synthesis of plakotenin, a cytotoxic marine natural product, using a biomimetic Diels-Alder reaction is described in detail. Two approaches were used, whereby the Diels-Alder reaction occurs at different stages of the synthesis. Homo- and nor-plakotenin, related natural products, were also prepared, as well as iso-plakotenin, a diastereoisomer of plakotenin. The syntheses prove the relative and absolute stereochemistry of the latter. The chemical biology of the plakotenins was investigated on selected compounds. PMID:23037572

Bourcet, Emmanuel; Kaufmann, Larissa; Arzt, Stephanie; Bihlmeier, Angela; Klopper, Wim; Schepers, Ute; Bräse, Stefan

2012-10-04

446

Structure in turbulent mixing layers and wakes using a chemical reaction  

Microsoft Academic Search

Plane turbulent mixing between two streams of water which contained dilute chemical reactants was studied in a new blow-down water tunnel. In a diffusion-limited reaction, a pH indicator, phenolphthalein, in one stream mixed and reacted with a base, sodium hydroxide, in the other stream to form a visible reaction product. The product was found to exist, as expected, in concentrated

R. Breidenthal

1981-01-01

447

Analysis of parameter effects on chemical reaction coupled transport phenomena in SOFC anodes  

Microsoft Academic Search

Mass, heat and momentum transport processes are strongly coupled by internal chemical reforming reactions in planar design\\u000a solid oxide fuel cell (SOFC) anodes. In this paper, a three-dimensional computational fluid dynamics approach is applied to\\u000a simulate and analyze reforming reactions of methane and various transport processes in a duct relevant for SOFC anodes. The\\u000a results show that the anode duct

Jinliang Yuan; Yuan Huang; Bengt Sundén; Wei Guo Wang

2009-01-01

448

Analytical assessment of the oscillating chemical reactions by use chemiluminescence detection  

Microsoft Academic Search

This paper introduces the chemiluminescence (CL) detection in oscillating reaction-based determinations using the analyte pulse perturbation technique, a straightforward and expeditious approach to deriving quantitative analytical information from oscillating chemical reactions. The behavior of the H2O2–KSCN–CuSO4-NaOH oscillating system in the presence of luminol was examined by using the proposed detection method and the classical potentiometric technique. Some analytical and practical

Rafael Jiménez-Prieto; Manuel Silva; Dolores Pérez-Bendito

1997-01-01

449

Fast growth in phase-separating A-B-copolymer ternary mixtures with a chemical reaction  

Microsoft Academic Search

We study the dynamics of phase separation of a binary A-B- polymer mixture with copolymer C, which is produced by the reaction of two counterpart reactive polymers A and B at the interface via the chemical reaction A+B&rlhar2;C. For low interfacial energy between the A and B phases, where the copolymer prefers to locate at interfaces, we show that the

Yue-Jin Zhu; Yu-Qiang Ma

2003-01-01

450

Rapid chemical reaction techniques developed for use in investigations of membrane-bound proteins (neurotransmitter receptors)  

Microsoft Academic Search

New techniques for investigating chemical reactions on cell surfaces in the microsecond-to-millisecond time region are described. Reactions mediated by membrane-bound neurotransmitter receptors that control signal transmission between ?1012 cells of the nervous system are taken as an example. Cells with receptors on their plasma membrane are equilibrated with photolabile, biologically inactive precursors of the neurotransmitters. Photolysis of these compounds releases

George P. Hess

2003-01-01

451

Macrokinetic equations for a quasi-stationary chemical reaction occurring in a porous isothermal particle  

Microsoft Academic Search

Derivation of macrokinetic equations for the calculation of the process rate in the internal-diffusion region in reactions in porous catalysts during regeneration is the topic of this report. Macrokinetic equations for a quasi-stationary chemical reaction occuring in a porous isothermal particle (i.e. combustion of solid deposits such as coke and tar) are presented. A mathematical model is presented which approximately

Yu. M

1982-01-01

452

Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction  

ERIC Educational Resources Information Center

|Surprisingly, spectator ions are responsible for unexpected kinetics in the biphasic copper(II)-aluminum displacement reaction, with the rate of reaction dependent on the identity of the otherwise ignored spectator ions. Application of a published kinetic analysis developed for a reaction between a rotating Al disk and a Cu(II) ion solution to…

Sobel, Sabrina G.; Cohen, Skyler

2010-01-01

453

Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction  

ERIC Educational Resources Information Center

Surprisingly, spectator ions are responsible for unexpected kinetics in the biphasic copper(II)-aluminum displacement reaction, with the rate of reaction dependent on the identity of the otherwise ignored spectator ions. Application of a published kinetic analysis developed for a reaction between a rotating Al disk and a Cu(II) ion solution to the…

Sobel, Sabrina G.; Cohen, Skyler

2010-01-01

454

Note on the stochastic theory of a self-catalytic chemical reaction. II  

Microsoft Academic Search

The general results of article I on the stochastic representation of the macroscopic stationary state of a self-catalytic chemical system are applied to a step-by-step chemical reaction. The relaxation times to the quasi-stationary state and to the final stationary state are computed by evaluating the first two non-trivial eigenvalues of the transition matrix. The previous results of Oppenheim, Shuler and

S. Dambrine; M. Moreau

1981-01-01

455

A stronger necessary condition for the multistationarity of chemical reaction networks.  

PubMed

Biochemical reaction networks grow bigger and bigger, fed by the high-throughput data provided by biologists and bred in open repositories of models allowing merging and evolution. Nevertheless, since the available data is still very far from permitting the identification of the increasing number of kinetic parameters of such models, the necessity of structural analyses for describing the dynamics of chemical networks appears stronger every day.Using the structural information, notably from the stoichiometric matrix, of a biochemical reaction system, we state a more strict version of the famous Thomas' necessary condition for multistationarity. In particular, the obvious cases where Thomas' condition was trivially satisfied, mutual inhibition due to a multimolecular reaction and mutual activation due to a reversible reaction, can now easily be ruled out.This more strict condition shall not be seen as some version of Thomas' circuit functionality for the continuous case but rather as related and complementary to the whole domain of the structural analysis of (bio)chemical reaction systems, as pioneered by the chemical reaction network theory. PMID:24048547

Soliman, Sylvain

2013-09-19

456

Detection of chemical weapon agents and simulants using chemical ionization reaction time-of-flight mass spectrometry.  

PubMed

Chemical ionization reaction time-of-flight mass spectrometry (CIR-TOF-MS) has been used for the analysis of prepared mixtures of chemical weapon agents (CWAs) sarin and sulfur mustard. Detection of the CWA simulants 2-chloroethyl ethyl sulfide, triethyl phosphate, and dimethyl methyl phosphonate has also been investigated. Chemical ionization of all the agents and simulants was shown to be possible using the CIR-TOF-MS technique with a variety of reagent ions, and the sensitivity was optimized by variation of instrument parameters. The ionization process was found to be largely unaffected by sample humidity levels, demonstrating the potential suitability of the method to a range of environmental conditions, including the analysis of CWAs in air and in the breath of exposed individuals. PMID:17894471

Cordell, Rebecca L; Willis, Kerry A; Wyche, Kevin P; Blake, Robert S; Ellis, Andrew M; Monks, Paul S

2007-09-26

457

Using chemical tracers in hillslope soils to estimate the importance of chemical denudation under conditions of downslope sediment transport  

NASA Astrophysics Data System (ADS)

We present a model of hillslope soils that couples the evolution of topography, soil thickness, and the concentration of constituent soil phases, defined as unique components of the soil with collective mass equal to the total soil mass. The model includes both sediment transport and chemical denudation. A simplified two-phase model is developed; the two phases are a chemically immobile phase, which has far lower solubility than the bulk soil and is not removed through chemical weathering (for example, zircon grains), and a chemically mobile phase that may be removed from the system through chemical weathering. Chemical denudation rates in hillslope soils can be measured using the concentration of immobile elements, but the enrichment of these immobile elements is influenced by spatial variations in chemical denudation rates and spatial variations in the chemical composition of a soil's parent material. These considerations cloud the use of elemental depletion factors and cosmogenic nuclide-based total denudation rates used to identify the relationship between physical erosion and chemical weathering if these techniques do not account for downslope sediment transport. On hillslopes where chemical denudation rates vary in space, estimates of chemical denudation using techniques that do not account for downslope sediment transport and spatial variations in chemical denudation rates may be adequate where the chemical denudation rate is a significant fraction of the total denudation rate but are inadequate in regions where chemical weathering rates are small compared to the total denudation rate. We also examine relationships between transient mechanical and chemical denudation rates. Soil particle residence times may affect chemical weathering rates, and the relationship between total landscape-lowering rates and soil particle residence times can thus be quantified.

Mudd, Simon Marius; Furbish, David Jon

2006-06-01

458

Ion-molecule reactions and chemical composition of emanated from herculane spa geothermal sources.  

PubMed

The paper presents a chemical composition analysis of the gases emanated from geothermal sources in the Herculane Spa area (Romania). The upper homologues of methane have been identified in these gases. An ion-molecule reaction mechanism could be implicated in the formation of the upper homologues of methane. The CH(4) (+) ions that appear under the action of radiation are the starting point of these reactions. The presence of hydrogen in the emanated gases may be also a result of these reactions. PMID:19325844

Cosma, Constantin; Suciu, Ioan; Jäntschi, Lorentz; Bolboac?, Sorana D

2008-06-20

459

Energy and Chemical Change - Energy Disposal and Energy Requirements of Chemical Reactions.  

National Technical Information Service (NTIS)

A new method, based on information-theoretic considerations has been introduced to help formulate questions and obtain model-free answers for the role of energy in the chemical change. Measures for the selectivity of energy consumption, the specificity of...

R. D. Levine

1974-01-01

460

Effects of Chemical Reaction and Double Dispersion on Non-Darcy Free Convection Heat and Mass Transfer  

Microsoft Academic Search

In this article, the effects of chemical reaction and double dispersion on non-Darcy free convection heat and mass transfer\\u000a from semi-infinite, impermeable vertical wall in a fluid saturated porous medium are investigated. The Forchheimer extension\\u000a (non-Darcy term) is considered in the flow equations, while the chemical reaction power–law term is considered in the concentration\\u000a equation. The first order chemical reaction

M. F. El-Amin; W. A. Aissa; Amgad Salama

2008-01-01

461

The spliceosome catalyzes debranching in competition with reverse of the first chemical reaction.  

PubMed

Splicing of nuclear pre-mRNA occurs via two steps of the transesterification reaction, forming a lariat intermediate and product. The reactions are catalyzed by the spliceosome, a large ribonucleoprotein complex composed of five small nuclear RNAs and numerous protein factors. The spliceosome shares a similar catalytic core structure with that of fungal group II introns, which can self-splice using the same chemical mechanism. Like group II introns, both catalytic steps of pre-mRNA splicing can efficiently reverse on the affinity-purified spliceosome. The spliceosome also catalyzes a hydrolytic spliced-exon reopening reaction as observed in group II introns, indicating a strong link in their evolutionary relationship. We show here that, by arresting splicing after the first catalytic step, the purified spliceosome can catalyze debranching of lariat-intron-exon 2. The debranching reaction, although not observed in group II introns, has similar monovalent cation preferences as those for splicing catalysis of group II introns. The debranching reaction is in competition with the reverse Step 1 reaction influenced by the ionic environment and the structure of components binding near the catalytic center, suggesting that the catalytic center of the spliceosome can switch between different conformations to direct different chemical reactions. PMID:23681507

Tseng, Chi-Kang; Cheng, Soo-Chen

2013-05-16

462

A kinetic model for chemical reactions without barriers: transport coefficients and eigenmodes  

NASA Astrophysics Data System (ADS)

The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solutions of the Boltzmann equations are determined through an expansion in Sonine polynomials up to the first order, using the Chapman-Enskog method, in a chemical regime for which the reaction process is close to its final equilibrium state. The non-equilibrium deviations are explicitly calculated for what concerns the thermal-diffusion ratio and coefficients of shear viscosity, diffusion and thermal conductivity. The theoretical and formal analysis developed in the present paper is complemented with some numerical simulations performed for different concentrations of reactants and products of the reaction as well as for both exothermic and endothermic chemical processes. The results reveal that chemical reactions without energy barrier can induce an appreciable influence on the transport properties of the mixture. Oppositely to the case of reactions with activation energy, the coefficients of shear viscosity and thermal conductivity become larger than those of an inert mixture when the reactions are exothermic. An application of the non-barrier model and its detailed transport picture are included in this paper, in order to investigate the dynamics of the local perturbations on the constituent number densities, and velocity and temperature of the whole mixture, induced by spontaneous internal fluctuations. It is shown that for the longitudinal disturbances there exist two hydrodynamic sound modes, one purely diffusive hydrodynamic mode and one kinetic mode.

Alves, Giselle M.; Kremer, Gilberto M.; Marques, Wilson, Jr.; Jacinta Soares, Ana

2011-03-01

463

Organo- and nano-catalyst in greener reaction medium: Microwave-assisted expedient synthesis of fine chemicals  

EPA Science Inventory

The use of emerging microwave (MW) -assisted chemistry techniques is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. A brief account of our experiences in developing MW-assisted organic transformations, which invo...

464

Charge exchange and chemical reactions with trapped Th{sup 3+}  

SciTech Connect

We have measured the reaction rates of trapped, buffer gas cooled Th{sup 3+} and various gases and have analyzed the reaction products using trapped ion mass spectrometry techniques. Ion trap lifetimes are usually limited by reactions with background molecules, and the high electron affinity of multiply charged ions such as Th{sup 3+} make them more prone to loss. Our results show that reactions of Th{sup 3+} with carbon dioxide, methane, and oxygen all occur near the classical Langevin rate, while reaction rates with argon, hydrogen, and nitrogen are orders of magnitude lower. Reactions of Th{sup 3+} with oxygen and methane proceed primarily via charge exchange, while simultaneous charge exchange and chemical reaction occurs between Th{sup 3+} and carbon dioxide. Loss rates of Th{sup 3+} in helium are consistent with reaction with impurities in the gas. Reaction rates of Th{sup 3+} with nitrogen and argon depend on the internal electronic configuration of the Th{sup 3+}.

Churchill, L. R.; DePalatis, M. V.; Chapman, M. S. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States)

2011-01-15

465

Electronically excited molecules: Reaction kinetics and emission of light: Nanosecond infrared spectroscopy, electronic emission from chemical reactions  

NASA Astrophysics Data System (ADS)

A time-resolved IR absorption spectrometer capable of detecting chemical transients on the nanosecond timescale was designed, constructed, and successfully implemented. The spectrometer was used to characterize the vibrational relaxation of an open shell radical species, CF3, produced with excess energy from the photolysis of the parent CF3I compound. The effects of vibrational excitation in the CF3 radical on the reaction CF3 + Br2 yields CF3Br + Br were measured. Broadband data collection techniques were used to monitor the reactive and relaxation pathways simultaneously. The energetic radicals react no faster than the thermalized CF3 and may actually have a lower cross section for reaction. The spectrometer was also used to detect the gas phase absorption spectra of the polyatomic radicals. A thorough investigation into ozone-olefin reactions in a cryogenic matrix environment was completed. It was possible to complex ozone with various olefinic partners through careful control of the matrix deposition process, despite the very low (1-5 kcal/mole) activation energies for the ozonolysis reactions. The ground state complexes were observed to form a charge-transfer (CT) complex upon excitation.

Moore, C. B.

1992-02-01

466